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| Can I manually manipulate my idle speed? (Page 4/10) |
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Romsk
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APR 20, 07:44 PM
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Do you know for sure if you have a factory ECM and the correct PROM?
I was in another thread and I mentioned this:
The ECM Model number must match:
Fiero Model
Year
Engine Size
The PROM in the ECM has a Model number and it must match:
The Tire Sizes
The Emissions: Federal or California
Transmission Type: Manual or Automatic
Transmission Gear Ratios (part of the Transmission Model)
If you have the correct ECM but the PROM is wrong, this could effect the Idle Speed which, on your Fiero, should be about 900 RPM fully warmed up with slight wavering plus or minus 50 RPM.
How the O2 Sensor is working can effect idle. An engine may run well with one that us starting to go or another problem may be present.
Here is a simple go/no go test:
Cold start.
Put the ECM in DMDIAG Mode (the Paperclip Trick).
Start the car (do not drive in this mode as the Timing Advance is disabled so you can set the timing to 10 degrees BTDC and not fight the ECM).
The Idle is forced to 1000 RPM (to help calibrate the Tachometer).
The SES should blink rapidly to indicate the ECM is in Open Loop.
After a few minutes, the O2 Sensor should be warm enough to start operating. This is when the ECM will go into Closed Loop.
In Closed Loop the SES should blink slowly (on and off every couple of seconds). The ECU constantly wavers the Air Fuel Ratio (AFR) slightly to make sure the O2 sensor is working and responding properly. When the light is on, the AFR is above 14.7 : 1 stoichiometric, and off when below that. So not only should it blink on and off slowly every second or so, it should also be about a 50% duty cycle on average. It's not perfect, but if it is not on and off about the same amount (50% duty cycle), something is effecting the idle AFR and that is a clue to a malfunction somewhere - possibly a sluggish O2 Sensor, or EGR Subsystem issue, dirty IAC Valve pintle and seat, flaky CTS Sensor. But you will be amazed on what other things that can effect Idle. One thing overlooked... a PCV Value... they get so oil fouled at times.
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Paul Romsky
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Kitskaboodle
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APR 20, 09:39 PM
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Thanks for the input Paul. You brought up some interesting things. This high idle issue has not always been there so I don’t think it’s computer related. Believe it or not, I change my 02 sensor every two years right before I get my smog test. Regarding a clogged pcv valve: would that apply in my situation since it does initially go high when cold (2500 rpm) but it does eventually go down to about 1400.
On a different note, I put in the new IAC today and basically it made no difference. It still idles at 2450-2500 when cold, takes a good 4+ minutes to go down and even so, it will only go to go 1350-1400 idle and about 1250 in drive. This is as low as it gets. 🙁
Here’s what I have done thus far:
Verified that engine dies immediately if I suddenly block off the throttle body opening
Replaced coolant sensor
Replaced IAT
Replaced IAC (Gumout used in IAC passage, proper reset done and drove it on freeway for about 30 minutes.
Not sure what to do next..,, 🙁
Kit[This message has been edited by Kitskaboodle (edited 04-20-2025).]
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Patrick
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APR 20, 10:36 PM
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| quote | Originally posted by Kitskaboodle:
Verified that engine dies immediately if I suddenly block off the throttle body opening
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That's fine for addressing concerns of a vacuum leak downstream from the TB. The problem with that method is that it doesn't tell you if the throttle blade itself is actually closing far enough. Instead of covering the entire mouth of the TB, just use your finger to block the port in the mouth of the TB that supplies air to the IAC valve.
The engine should stall. If it doesn't, I'd suspect that the idle stop screw is misadjusted (or the throttle linkage is hanging up somewhere). If it does stall, then see below.
| quote | Originally posted by Kitskaboodle:
Replaced....
Replaced...
Replaced...
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Kit...The problem, as I see it, is that you're not investigating what if any difference the new sensors are doing in regards to the actual info they're sending the ECU. If you don't use a scanner or WinALDL, you're flying blind. It's possible for example that the new CTS or IAT sensor is telling the ECU that it's -40°. I'm not trying to give you a bad time, but it's the reality of the situation. You need to know what the ECU is being told. It's even possible the wiring harness has an issue which is preventing one or more sensors from telling the ECU anything. In theory a code should be set if that's the case, but I'd want to know for sure what's going on.[This message has been edited by Patrick (edited 04-20-2025).]
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Vintage-Nut
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APR 21, 10:49 AM
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Romsk
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APR 21, 12:20 PM
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Kit,
It might feel like we are coming at you from all sides, well, we kind of are - from all over the world [smile]. But it's just hard for a bunch of people to make suggestions in a forum. If we were all there with you, this would be a whole bunch simpler. If someone tells you to do something you already did, just ignore it [smile] It's happens to all of us. Hang in there, we will do our best to help you.
I saw your list and you seem to be doing the right things so far. One of the things about this site, I can't see any of the message as I type a reply, so I can't keep the whole thread in my head, so I might get redundant or miss something.
There is a lot more things to look at, but I try to suggest the simpler things first. I am a "pull it and bench test it" kind of guy... I don't like to "replace things until it works".
I believe you when you say there are no vacuum leaks. I am old school and used the carb cleaner trick to find leaks... effective but DANGEROUS - don't do it. They now make fog generators that are very safe and can help find the more subtle leaks. Look into them but don't buy one just yet.
You are in the right area:
Throttle Body:
Throttle Plate: closed/open/sticky/dirty/obstructed/loose-worn bearing
IAC: Valve Seat clean and IAC Unit replaced (hard to test on the bench without using an Arduino UNO and a stepper motor driver).
TPS: Adjusted properly, not noisy (signal wise), not sticky. I can tell you how to bench test one (even if it is new... we see a lot of failed out of the box these days).
Cold Start Fuel Valve and it's Temperature Switch (near the Fan Switch). The injector can leak, the Switch can get flaky. A bit involved to bench test the Injector.
MAP Sensor: Can tell you how to bench test it.
EGR Solenoid: Again, bench testing may help rule it out.
EGR Valve, I agree with the others, a subtle leak or stuck valve can affect Idle. I have instructions on bench testing the EGR system.
CTS: You replaced it. I recommend bench testing first it before installing - we can revisit that later.
IAT: You replaced it. Bench test first - but we can revisit that later too if needed.
PCV Valve: Involved to bench test, not expensive, best to replace at every tuneup before emissions... California or Federal?
Fan Switch: Most likely not and issue with idle, but you need to make sure it is working. There are 2 Fans: one on the Radiator, one behind the rear trunk liner on the passenger side. This hidden fan keeps the Ignition Coil and Alternator cool. Critters like to build nests in the fan. I have tips to prevent that. Needs to be checked yearly.
Air Filter: I think you have that covered.
Coolant Thermostat: Involved to bench test. Watch your dash Temperature Guage, but don't rely on it. The guage is driven by the ETS (Engine Temperature Sensor) on the head near the distributor. It's is separate from the CTS.
If you have Cruise Control, is it functioning properly? A subtle leak here could affect idle in rare cases.
I don't think you need to look at the Ignition System yet.
Now the harder things to put off on checking until everything else is ruled out.
Fuel Pump: Not working efficiently. Too difficult to remove for normal bench testing.
Fuel Pressure: Not around 40 PSI +/- 5. Wider tolerance may be ok.
Fuel injector: Leaky. Involved to get at and more involved to bench test.
Having a scan tool is vital in diagnostics. Many of the sensors can be ruled out by using a good one.
I designed the Fiero GT ALDL Monitor Adapter that is sold from The Fiero Store. The GUI software is free to download and to look at, but the Adapter costs $84.95. Be careful with any ALDL Tool. They can only give you indications, they usually don't solve all problems, but they help. Fieros don't have OBD-II, so the ALDL is all we have.
If you have the budget and you buy my Adapter, I will help you as much as I can using the tool and what it is telling you. If money is tight, I don't recommend buying it.
I am in New Hampshire USA in the eastern time zone. I am available for free phone consultations from 9AM to 9PM 7 days a week, but send me an email first to set up a phone call. You pay for the call.
My email is on my webpage:
Paul Romsky Fiero GT ALDL Monitor
Paul
+1(603)465-7225
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Paul Romsky[This message has been edited by Romsk (edited 04-21-2025).]
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Romsk
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APR 21, 12:47 PM
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For my own edification:
Are you checking Idle RPM using the Fiero's Dashboard guage, or with a Ignition Tool?
When you put the ALDL in DMDIAG Mode, one of the things it does it force the idle to 1000 RPM. It may waver but the ECM will try to hover around 1000 on average.
Use the Paperclip trick to put the ECM in DMDIAG Mode, don't drive in this mode, the Timing Advance is disabled so you don't fight the ECM setting it to 10 degrees BTDC.
The Fiero Tachometers are around 40 years old now. Capacitors in their circuitry are starting to drift way out of tolerance. There are ways to recalibrate the Tachometer, but it requires a small circuity change. Leave that for later, a good Ignition Tachometer Tool or ALDL Tool will give you more accurate readings.[This message has been edited by Romsk (edited 04-21-2025).]
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Kitskaboodle
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APR 21, 07:17 PM
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Wow, you guys are tag teaming me. But, I say that it’s a good thing. 😊
Hope I can remember all that was said above.
Patrick- yes, you’re correct. I can test things rather than simply replace but I just wanted to be done with it and was hoping my “quick fixes”would work.
Funny interjection here: my dad was an aircraft engine inspector for United Airlines SFO and so I heard a lot of stuff from him that he learned and wanted to school me on. I always remembered this saying: “There’s never enough time to do it right, but there’s always enough time to do it over”. Hmmm, I think that applies to my Fiero method of repair technique. 🙁
Ok, on to business….
Patrick- I was thinking that very thing yesterday about the possibility of the throttle body butterfly not closing all the way. So, I examined the opening and looked closely top and bottom while turning the throttle shaft and it seems to be fully closing. While I had the rubber snorkel off I decided to hit the throat area with Gumout and also hit the orifice hole. At this point I did not start the car yet as I was also in the process of removing, cleaning and testing the pcv valve as mentioned above. (doesn’t hurt to check it) After hitting it with Gumout, I made sure the barrel doohickey rattled around inside. Then I did the blow test. Here’s the weird part: as you know it’s supposed to allow air one direction only but I noticed it will still occasionally blow in both directions. I think that barrel thingy doesn’t always seat properly. (a little flaky?) Anyways, since a metal AC Delco is only $6 bucks, I’m just going to put in a new one. This is where I stopped for the day. I will get the pcv valve tomorrow afternoon. As soon as I get it I will install it and then start car (from cold) and put my finger over the hole in the throttle body and see if it dies and then report back.
Vintage- Nut: I do have 3 spare MAP’s. One is an
good used GM factory one but I don’t see a GM p/n on it. I will do a swap tomorrow and see what the fully warm idle it is. (right now it’s 1400 when fully warm)
Paul: Strangely enough, I tried to buy the scan tool from the FieroStore website about 4-5 months ago and I didn’t see it. Today I looked and now they have it again. It’s gone up to the tune of $114.95 🙁 Cooling system is fine. Car runs consistently cool / normal. Thermostat is ok. Fan has been upgraded to electric and comes on no problem. Water pump is brand new as well as the fuel pressure regulator. As for the tach, it’s always been consistent as far as I know and in the past I installed Rodney’s tach filter. Actually, I do have a timing light with a built in tach but I’ve not used it on this car.
After I do all that I said above, I want to address the egr valve as you guys pointed to. I do have a Mighty Mite vacuum gauge / Kit. So, when the engine is cold, is the egr supposed to be open or closed? And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust.
No, on my egr you cannot really see the plunger in action.
Thanks everyone for your input!! 😊
Kit[This message has been edited by Kitskaboodle (edited 04-21-2025).]
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Patrick
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APR 21, 08:30 PM
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| quote | Originally posted by Kitskaboodle:
I was thinking that very thing yesterday about the possibility of the throttle body butterfly not closing all the way. So, I examined the opening and looked closely top and bottom while turning the throttle shaft and it seems to be fully closing.
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There's no way the engine is going to be idling at all unless air is getting in somewhere. Since you already know that there is no vacuum leak downstream of the TB, plugging the IAC port with your finger will tell you whether the unwanted air is getting past the throttle blade. If the engine stalls with the IAC port blocked, then you'll know for sure that the IAC valve is letting too much air in... for reasons yet to be determined.
| quote | Originally posted by Kitskaboodle:
I want to address the egr valve as you guys pointed to. I do have a Mighty Mite vacuum gauge / Kit. So, when the engine is cold, is the egr supposed to be open or closed? And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust. No, on my egr you cannot really see the plunger in action.
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The EGR valve only opens under certain conditions while driving. On the OEM style EGR valves, you can actually open the valve by hand by sticking a finger up through a hole on the underside of the valve housing and pushing the valve open. The engine will stumble (while idling). If your EGR valve does not have the holes in the underside of the EGR housing, a vacuum pump will open the valve... and again, the engine should stumble. However, I don't feel your elevated idle RPM speed is EGR related.[This message has been edited by Patrick (edited 04-22-2025).]
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Vintage-Nut
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APR 21, 08:33 PM
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| quote | | is the egr {valve} supposed to be open or closed {at idle?} |
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Closed
| quote | | And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust. No, on my egr you cannot really see the plunger in action. |
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Yes, you can't verify if it’s stuck open due to carbon deposits when it’s bolted to the exhaust, BUT you can check the diaphragm "in action"..
While the engine is cold:
*Remove the vacuum line from the EGR vacuum port
*Connect your hand held vacuum pump with gauge on the EGR vacuum port
*Apply vacuum and observe the EGR diaphragm/valve, the valve should move up
*Hold the pressure a minute or two...the pressure must hold / if not, the diaphragm has a hole and replace the EGR valve.
If you need to replace the EGR valve:
How to Replace Your V6 EGR Valve - Step by Step by Bloozberry
https://www.fiero.nl/forum/Forum9/HTML/000033.html[This message has been edited by Vintage-Nut (edited 04-21-2025).]
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Romsk
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APR 22, 12:38 AM
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Kit,
My adapter is the $84.95 one. It is called the Fiero GT ALDL Monitor.
86-88 V6 ECM ALDL Monitor Tool[This message has been edited by Romsk (edited 04-22-2025).]
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