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The Quest For the Perfect Idle Continues... by HummelHund
Started on: 12-02-2003 01:18 AM
Replies: 107
Last post by: USFiero on 05-07-2006 10:07 AM
HummelHund
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Report this Post12-02-2003 01:18 AM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Ok, so far, in trying to get my 88' Coupe, 2.5L to run smoothly, I have replaced:
MAP Sensor
MAT Sensor
O2 Sensor
Coolant Temp. Sensor (replaced by prev. owner)
EGR Valve
All vaccuum hoses
Plugs (AC Delco)
Wires
Fuel Filter
Oil & Oil Filter
Air Filter
I've also decarbonized the engine using Ed Park's three part system.

Still, after all this, the car runs rough at startup, and once warm, the idle hunts and the car sort of coughs/hiccups. I've also noticed that under hard acceleration (I was in 3rd gear at the time, if that helps), it stumbles a little. The engine has good oil pressure and doesn't leak anything.

So. What's next to replace? My top suspects are:

Wires- I bought Autozone wires, which I haven't had problems with in the past, but those cars were not DIS.

Fuel Vapor Canister- It's original, maybe a source of vaccuum leak?

DIS Parts- A long shot, because from what I've read, they either work or they don't.

A PROM Problem- I was alerted to this GM TSB in another thread. Apparently the PROM can be a problem with these late model Fieros, and sometimes need to be changed? Anyone have any ideas on that? Link to the discussion: //www.fiero.nl/forum/Forum2/HTML/043407.html

The only other problem with the car is noisy timing gears. Could they be worn enough to cause erratic idle and the hiccups?

I am bound and determined to get to the bottom of this. Help!

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camon
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Report this Post12-02-2003 03:37 AM Click Here to See the Profile for camonSend a Private Message to camonDirect Link to This Post
Not sure as I don't own a 4cyl. but does your car have a TPS. If so that would be something I would concider replacing if not done yet!

I have noticed after replacing mine that I get a nice smooth idle (800-850rpms). My car (87 GT) also use to suffer from a very poor running condition when cold (it would stumble and hesitate while taking off). My car suffered from this for the better part of a year.....and I threw everything at it that I thought would correct it (plugs,wires,o2,egr,air filter,injectors,distribitor with rotor and cap, timming adjustments,even fuel filter and pump) but nothing did......so I gave up, that is until I decided to swap out the TPS from my 86 GT and low and behold it solved the problem and the real kicker was "I didn't even do it to solve this problem...I was trying to cure a high idle issue on the 86GT and was trying to rule this out".

Good luck!

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HummelHund
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Report this Post12-02-2003 03:47 AM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
It does have a TPS. I had sort of ruled that out in my head due to a lack of any codes, but it is a possibility I need to look into.
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camon
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Report this Post12-02-2003 04:12 AM Click Here to See the Profile for camonSend a Private Message to camonDirect Link to This Post
My 87 wasn't throwing any codes either so that was why I never considered it either. It was a surprise when I seen it fixed the 87 but at the same time upset me that it didn't fix the 86. Although the 86 problem is fixed now aswell (seems that when I pulled the plenum off to pull a head that I forgot to hookup a vaccum hose).

Not sure if there is anyway to test it or not either (short of buying one....and that would suck if it not your problem).

Good luck!

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Report this Post12-02-2003 08:46 AM Click Here to See the Profile for PyrthianSend a Private Message to PyrthianDirect Link to This Post
I just replaced my alternator recently, and it got rid of my hunting idle. I have a underdrive pulley, and when my alternator died, I replaced it with a higher output alternator (SI to CS conversion) and it solved my hunting idle. But I had really LLOOOWW output before with the SI alternator. wipers would barely make it across the windshield at idle. But, anyways, ground & power will affect idle. See what your output from your alternator is at idle.
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cool-tom
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Report this Post12-02-2003 09:20 AM Click Here to See the Profile for cool-tomSend a Private Message to cool-tomDirect Link to This Post
I have had idle problems and tested my TPS with an ohm meter. IIRC it showed 0 ohms to 5000 ohms in a smooth steady sweep. As I moved the TPS the meter followed every move, so I concluded it was working OK.
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Report this Post12-02-2003 09:51 AM Click Here to See the Profile for EMFORCESend a Private Message to EMFORCEDirect Link to This Post
I recently had my timing gears and chain replaced (3.4L) and it seemed to help the idle a lot once warmed up. But, still , every once and awhile it decides to idle at 1500- 2000 RPM. there is no rhyme or reason to this- but it happens infrequently.

------------------
EMFORCE
'88 Formula (Silver)
3.4 L, 5-speed
Performance tires/wheels, sound system, electrics, exhaust, etc. (man I NEED new seats!!)

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Report this Post12-02-2003 11:19 AM Click Here to See the Profile for rubeSend a Private Message to rubeDirect Link to This Post
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HummelHund
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Report this Post12-02-2003 03:40 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
I don't think the alternator's the problem. Output is fine, and the unit itself is pretty new. I will check the grounds, though, that could definitely cause some idle trouble.

rube- Thanks for the link. The injector troubles mentioned in there seem like a very reasonable answer, I think AC Delco plug wires and a new injector are on my shopping list.

Thanks guys, keep the suggestions coming! If we can get all the possible reasons for a bad idle in here, it'll help me, and future Fiero owners!

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Report this Post12-02-2003 04:15 PM Click Here to See the Profile for TaurusThugSend a Private Message to TaurusThugDirect Link to This Post
have you tried timing or oil?

------------------
'86 Fiero GT


www.KylesFiero.tk

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HummelHund
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Report this Post12-02-2003 04:33 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
You can't adjust the timing on an 88' Coupe, and the oil and filter have been changed. Thanks for the suggestions, though.
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HummelHund
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Report this Post12-02-2003 08:47 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post

HummelHund

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Ok, went to Autozone and bought a new injector. I'll post the results tomorrow. Wish me luck!
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ManiMack
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Report this Post12-02-2003 10:32 PM Click Here to See the Profile for ManiMackSend a Private Message to ManiMackDirect Link to This Post
88's dont have IAC's do they? Because they can be a prob.
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HummelHund
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Report this Post12-02-2003 10:48 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
They do, that had slipped my mind. I think they can be tested, though, I'll have to look into that.
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Report this Post12-04-2003 01:31 AM Click Here to See the Profile for rubeSend a Private Message to rubeDirect Link to This Post
I doubt it's the IAC. Been there, done that. Done lot's of stuff actually. The IAC is one of those things that if it wasn't working you'd know it. If you hook up a cheap air/fuel ratio meter it will probably show wide swings at idle in time with the hunting.

Vaccum leak is probably out too, that would tend to be continuous. Gotta be fuel delivery somewhere.

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HummelHund
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Report this Post12-04-2003 01:48 AM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Thanks for the tip. The Ogre seems to back you up, from the article on the 700 TBI in his cave. He does mention a tester you can use for the IAC, if everything else is ruled out, I'll go that route.

Well, I didn't have a chance to change the injector out today, and now it's raining. The forecast is for rain tomorrow, as well. Having no garage or carport doth suck royally.

When the weather allows, I'll put the new injector in and post the results.

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HummelHund
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Report this Post12-05-2003 12:06 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
And the Quest continues...

The injector didn't help with the idle, or the hiccup/cough/sputtering. Tomorrow I'm going to order some AC Delco plug wires(no one around here has them) and doublecheck my spark plug gap. I'll continue to post results to this thread, maybe my mistakes will help someone else further down the road.

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OutlawFiero
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Report this Post12-05-2003 11:58 PM Click Here to See the Profile for OutlawFieroClick Here to visit OutlawFiero's HomePageSend a Private Message to OutlawFieroDirect Link to This Post
yep, it will. Because I'm in the same boat, with exact same problem. I will post what I try tomorrow.
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Report this Post12-06-2003 01:13 PM Click Here to See the Profile for beachbombSend a Private Message to beachbombDirect Link to This Post
I had almost the same problems on my '84Indy, mine would always hunt for idle and idle high(around 1300rpm), after replacing everything you did and even more, i finally replaced the rubber gasket that is on top of the valve cover, that(i think) went to the pcv valve hose. After replacing, car idled perfect!!! Ran a little better too. Not sure if this is you problem, but it could help, good luck!..jim('86GT)
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Report this Post12-06-2003 02:08 PM Click Here to See the Profile for BruceSend a Private Message to BruceDirect Link to This Post
Check the archives for the past month or so. I think someone ($Rich$ ?)posted that he ran a ground wire from someplace to another (no charge for the technical jargon), and that really smoothed out his idle. It was a simple ane effective fix.
b
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HummelHund
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Report this Post12-07-2003 04:11 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Ok, today I checked spark plug gap. A couple of the plugs were a little off, but fixing this did not solve my idle problem. I've got some plug wires on order, and they should be in tomorrow.

I'd noticed that sometimes when I turned my car on after letting it sit for just a few minutes, the idle would race up to 2500rpm, then after a 15-30 seconds, would come back down, and the SES light would come on. Today, the Fiero and I had a chat through its SES light, and I got these codes:

Code 13: Oxygen Sensor
I've replaced the O2 sensor! Mayhaps the sensor's just confused.

Code 36: IAC
Hmm....perhaps ManiMack was on to something...

Code 44: Lean exhaust
Points to the O2 sensor and/or a vaccuum leak. The Haynes manual mentions the TBI base gasket. Mine is a little ratty, I may have to try replacing that.

Any tips based on my findings today?

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Report this Post12-07-2003 05:41 PM Click Here to See the Profile for OutlawFieroClick Here to visit OutlawFiero's HomePageSend a Private Message to OutlawFieroDirect Link to This Post
I think our cars have esp or something because that is also what mine does, and with the same codes. When I find a good solution I will post. I did do the extra ground, and it did smooth the car a little more, but not the idle problem. Because of the higher idle does your car also read about 500 rpm to high at cruising speeds also? I keep thinking and the car acts like their is some problem with a system/sensor that is not reading properly. So it idles, then jumps a little, idles again (high) and then jumps, and this goes on and on. I know what you mean by saying it's not a vacumm leak, I have had that before and this is not it. Something is not reading properly, or sadly it might be our ecm going bad.
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Report this Post12-07-2003 07:47 PM Click Here to See the Profile for rubeSend a Private Message to rubeDirect Link to This Post
Check fuel pressure and flow.
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Report this Post12-07-2003 08:18 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreDirect Link to This Post
look for vac leaks. read that article in my cave. Don't overlook the spare fitting to the left of the TBI unit.

sweep the wiring, especially grounds. Read Wire Service in my cave. Don't just look at them. take the grounds off and check each one. Replace the braied strap and run it to solid metal, NOT the bloody hinge stud like GM did.

DO NOT assume the alt is ok! have that and the battery tested. This can be done in car at Autozone, Sears, NTB, and many other places for free.

------------------
Be alert. The world needs more lerts...

The Ogre's Fiero Cave (It's also at the top of every forum page...)

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HummelHund
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Report this Post12-07-2003 09:35 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Thanks guys. I'm going to give it another vacuum leak test, and then check the grounds. Come to think of it, the small battery to body ground that the Ogre speaks of in his cave isn't connected, I noticed that today.

I'll let y'all know how it works out.

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Report this Post12-07-2003 10:11 PM Click Here to See the Profile for jeffndebrusSend a Private Message to jeffndebrusDirect Link to This Post
I am sorry to hear that the 88 is giving you problems! Check the metal tubes that go to the fuel vapor cannister. I am not sure if these are "vacuum" or not, but I seem to remember corrosion at this point.
The 86 is slowly coming along. I fixed the horn and wipers-both grounding problems. Still have to replace the heater core so I will have heat and defrost. Still setting a code 32 egr even with the new egr and braided egr tube. Bled the clutch and it is shifting pretty well now. Still have to sort out the wiring mess from the alarm system. Maybe someday I can get the radio to work lol.
Good Luck!!
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HummelHund
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Report this Post12-07-2003 10:26 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
It's been a good car, it's just got a few annoying problems that won't go away. I noticed those tubes when I replaced the soft hoses that come from them, I guess I need to get a can of throttle body cleaner and check for leaks in that area. I just came in from connecting the loose ground, and the idle problem is still there, though it does seem to run a little smoother (might just be in my head, though ). I've been reading about the 86', man, I didn't know it had that much wrong with it! I wouldn't have traded my 87' GT + cash for it if I'd known that. Good to hear you've got it going, though.
You may want to take that EGR off and inspect it, make sure the last owner put it on right, especially if it isn't AC Delco. The aftermarket ones use a washer to fit properly, and if you don't get it on just right, it won't work. And the radio worked when I first got the car, then stopped working for no apparent reason. I didn't really look into why, maybe a fuse or wire connection?

One disturbing thing I noted while freezing outside, connecting that ground wire: My battery seems to be buzzing intermittently when the car is cooling down, then stops when it's completely cool. Is the battery going to explode? 'Cause if I have to have surgery to repair my face, I won't have the money to work on the Fiero.

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HummelHund
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Report this Post12-08-2003 08:04 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Replaced the plug wires today, with AC Delco OEM. The idle problem is still there. I'm going to check grounds and vaccuum lines as soon as I get a chance. I think I'm also going to pull off the coil pack and inspect it and the crank sensor. I'm sure it won't hurt to have a new coat of dialectric grease. Will post the results as they come...
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Report this Post12-10-2003 03:45 AM Click Here to See the Profile for rubeSend a Private Message to rubeDirect Link to This Post
Ummm...fuel? Seriously. An ignition system problem would most likely show itself as misfire/ backfire so I don't think that's your problem. Remote diagnosis is tough but I'd say look at the fuel pump.
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Report this Post12-10-2003 05:35 AM Click Here to See the Profile for GordoSend a Private Message to GordoDirect Link to This Post
My 88 coupe has always had a slightly erratic idle with occasional stumble right from the time it was purchased new from the dealer. It was returned twice under warranty and they replaced the TPS both times to no avail. To this day, 72,000 miles later it still idles the same way. I have always just considered it the normal "nature of the beast" as my wife's 88 coupe also idles the exact same way. We have no drivability problems. They both accelerate just fine with no hesitation under load.

I might add that over the years, I have changed plugs, wires, coils, map sensor, pcv and the entire computer. It still idles exactly the same.

------------------

[This message has been edited by Gordo (edited 12-10-2003).]

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HummelHund
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Report this Post12-12-2003 08:29 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
After a short break, the Quest continues...

rube- I'm listening to ya. Buying a fuel pressure gauge is on my list of things to try. I REAAALLY don't want to have to change another fuel pump, but if it comes to that, I can.

Tomorrow I'm going to double check for vacuum leaks. I'm also going to inspect the coil pack and regrease its baseplate, and check the crank sensor while I've got it off. I think I'm also going to order the replacement PROM specified in the GM TSB and try that.

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Report this Post12-13-2003 02:50 AM Click Here to See the Profile for rubeSend a Private Message to rubeDirect Link to This Post
I would save my money and not buy the updated PROM. Think about this. The car did not have the problems your having when it was new. Nobody would have bought it. So, the problem has to be elsewhere since the car ran acceptably at some point in it's life with the current PROM. Dropping the tank is a pain but it might be worth it in the long run.

I've often wished GM had provided an access panel of some sort to allow changing the pump from inside the car (like an Eclispe). I hate being under a car on jackstands. Gives me a creepy feeling.

Easter egging with new parts sucks but sometimes you don't have a choice.

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Report this Post12-13-2003 04:46 AM Click Here to See the Profile for numanSend a Private Message to numanDirect Link to This Post
Coolant Sensor, it aids in determining proper timing & fuel mix. Just a guess on my part.
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Report this Post12-13-2003 07:42 PM Click Here to See the Profile for ManiMackSend a Private Message to ManiMackDirect Link to This Post
Did you ever check the IAC?
My 84 had a bad IAC. The 84 engines are obviously a whole different beast in the 88. But it completely messed up the idle.

You could try taking it out an spining the cap in or out a tiny bit. If you can make the idle go down by doing one or the other it could be the prob.

This is just what I found from fixing my 84. Its idle was all over the place b4 I replaced it.

Good luck!

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Report this Post12-13-2003 08:02 PM Click Here to See the Profile for chcukSend a Private Message to chcukDirect Link to This Post
I had a similar problem with my 84. I chanegd the O2 sensor with an after market brand. I blamed everything else until an old GM mechanic told me to install an AC Delco O2 sensor. He was right. Lots of new prts for no reason. It's GM parts for me on ALL my cars now!
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Report this Post12-13-2003 08:28 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageSend a Private Message to Darth FieroDirect Link to This Post
Not to overstate the obvious, but have you done a compression and leakdown test? If you have poor sealing valves they can cause all kinds of problems that not only show up at idle, but could cause problems under full throttle as well. With all the electrical and sensor work you have done, I am thinking your problem could be mechanical.

------------------
power corrupts. absolute power corrupts absolutely.

Custom GM Chip Burning | Fiero Engine Conversions | Turbocharging | dtcc.cz28.com

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Report this Post12-13-2003 09:07 PM Click Here to See the Profile for West Coast FieroClick Here to visit West Coast Fiero's HomePageSend a Private Message to West Coast FieroDirect Link to This Post
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Report this Post12-13-2003 10:14 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
Once again, thanks for all the suggestions, this is helping a lot. It rained all day today, so I didn't get a chance to check for vacuum leaks. Tomorrow, if the weather's better, I will:

1. Check for vacuum leaks with throttle body cleaner.
2. Check and regrease all grounds.
3. Inspect DIS.
4. Inspect IAC.
5. Buy a compression tester/gauge and check compression.

I'll post my findings, we WILL get this thing running right!

Oh, and chcuk, I've used AC Delco parts as much as I can, including the O2 sensor, so I don't think that's the problem. Thanks for the suggestion, though!

[This message has been edited by HummelHund (edited 12-13-2003).]

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HummelHund
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Report this Post12-14-2003 04:38 PM Click Here to See the Profile for HummelHundSend a Private Message to HummelHundDirect Link to This Post
The compression test results are in:

#1 - 153
#2 - 160
#3 - 158
#4 - 170

They look like good numbers to me, any thoughts from the experts? I wasn't able to get any of the other tests done, other than a quick vacuum leak check that turned up nothing. I'm going to try to do a more thorough one when I get some time.

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Report this Post12-15-2003 02:18 AM Click Here to See the Profile for ryan.hessSend a Private Message to ryan.hessDirect Link to This Post
I'm not sure what the exact number is, but #1 is 10% lower than #4, which is a bit worrysome. However, two things come to mind that *need* to be checked/replaced, at least with some used junkyard parts to rule them out. TPS and IAC are two beasts that can test correctly and still be bad. (Okay, this is my opinion here, relating to experiences with a surging 93 grand am) TPS specifically has to be in a certain range or else the O2 will be so rich it'll set a code. IAC may be acting very slowly, causing a surging while it tries to match the idle rpm and "controlled vacuum leak". Hope this makes some sense, it's too early.
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