My '88 2.5L (5 speed) goes to almost 3000 rpm on a cold start-up then after 10 seconds drops to around 2000 rpm and after another 10 seconds (or so) drops to 1200-1300. Once it fully warmed up the idle is normal 900-1000 rpm.

Somehow I doubt they did this when new but my question is "is this normal"?

I have a couple that do the same thing and think nothing of it.

3,000 sounds high. 2,000 and I wouldn't think anything about it. I'd consider it only cosmetic however if you wish you can check the resistance of the Coolant Temperature Sensor and the Air Intake Temperature sensor. They check by reading the resistance pin to pin. You will want to check the resistance of the sensors when the engine is cold. It sounds like the resistance when warm has to be right (ish). Note - there is also a Temperature Gauge Sender - also a two pin sensor - that runs the temp gauge and has no effect on the operation of the engine. The only thing the Temp Gauge Sender connects to is the gauge itself.

I put my scan tool on it yesterday, The MAT and CTS both read around 70°F just after startup. I let it warm up a short time and the CTS climbed to around 175°F. I "think" the MAT climbed too, I'll have to recheck it and report back.

No need to report it.

That's how your ECM is programmed then.

If you really really want it to be different it's possible but not that easy. You can get someone to burn a chip for your existing ECM, or swap to a different ECM and then have someone program a chip for it.


http://gmtuners.com

is the place I would start however I don't know if he programs the ECM chips for the 2.5

He is DarthFiero on this board

Ryan

[This message has been edited by phonedawgz (edited 12-03-2010).]

So you're saying the Fiero came like that from the factory (3k rpm startup)?

Years ago I hade a '86 Camaro that I converted from carb to multiport EFI (tuned port) and burned by own chips for it. At first I used a MAF based 1227165 ECM but later I upgraded to a Speed Density (MAP) 1227730 ECM.
It had a high idle on startup too that I programmed out but it wasn't as high as the Fiero, it was only around 2000 rpm I believe. I still have my programming equipment out in my garage somewhere.

Well the ECM is working. The ECM isn't seeing an incorrect temp causing it to make the engine idle higher. The ECM can quite clearly control the IAC and thus the idle. The IAC is working. Unless you can come up with something that is leaking vacuum into the intake only during start up, there is no other conclusion.

The ECM on my 2.8 revs the engine too fast at start up in my opnion. I think that has a whole lot to do with the fact that these are some of the first ECM controlled cars GM made and GM thought they had to follow what they had learned about carbs. Later ECM's aren't programmed to rev the engines at start nearly as much.

idk, I surely could be wrong. Anyone else have anythign to say about the RPM's they are getting on their dukes at start up?

The only 4 cylinder Fiero I owned was to harvest the Izusu tranny from. It's only trip was when I drove it to my garage of Duke disembowlment.

87 dis duke also has a 3k rpm start up idle till I tap the gas and it drops. I also however know I have a phantom vacuum leak somewhere as my idle is about 3-4 hundred rpm high at all times after.

quote Originally posted by katore8105: 87 dis duke also has a 3k rpm start up idle till I tap the gas and it drops. I also however know I have a phantom vacuum leak somewhere as my idle is about 3-4 hundred rpm high at all times after.

Like 1300? You get a high idle SES light at long stop lights?

quote Originally posted by phonedawgz: Like 1300? You get a high idle SES light at long stop lights?

yes I do.

EDIT: to add, IT DRIVES ME NUTS!!! Can't find the bastard leak anywhere!

[This message has been edited by katore8105 (edited 12-03-2010).]

I wonder if my minimum air setting is correct? I jumpered pins A and B on the ALDL connector, turned key on and disconnected the IAC. Jumpering the ALDL should cause all sensors to max out. Disconnecting the IAC locks it at the max position, then the engine is started and the idle screw adjusted to lowest rpm possible.

I dug out all my old prom editing equipment. I use Tunercat and I do have a defination file for the '88 2.5L ecu. That's good news. Tomorrow I'll pull the prom and read/edit it if I find the correct setting for the startup rpm climb.

I will report back if I have any success. I may be able to help others too.

[This message has been edited by sportcoupe (edited 12-03-2010).]

quote Originally posted by sportcoupe: I wonder if my minimum air setting is correct? I jumpered pins A and B on the ALDL connector, turned key on and disconnected the IAC. Jumpering the ALDL should cause all sensors to max out. Disconnecting the IAC locks it at the max position, then the engine is started and the idle screw adjusted to lowest rpm possible. I dug out all my old prom editing equipment. I use Tunercat and I do have a defination file for the '88 2.5L ecu. That's good news. Tomorrow I'll pull the prom and read/edit it if I find the correct setting for the startup rpm climb. I will report back if I have any success. I may be able to help others too.

quote Jumpering the ALDL should cause all sensors to max out.

I have heard that before but have wondered what the line is supposed to mean. The only thing the ECM can 'max out' is the 'controls' not the sensors. The sensors 'read' conditions of the engine for the ECM to adjust it's controls. The things the ECM can control are IAC, the spark advance, the fuel injectors, the EGR solonoid, and the fuel pump. Not sure how anything execpt the IAC can be 'maxed out'.

The throttle stop screw is supposed to be adjusted to make the engine run at 500 rpm, not the 'lowest rpm possible'. Part of the reason for that is to keep the engine running if for whatever reason the IAC got set somewhere out of wack by the ECM. That is also with the engine warmed up.

Since the IAC can control the idle down to 1,000 rpm when warm, I don't see how the throttle stop screw could cause this problem. The engine should normally run slower when the engine is cold. The ECM adjusts the IAC to make it run faster. Since the ECM can slow the warmed engine down to 1,000 it seems unlikely the throttle stop can be the problem. That said it WILL be interesting to see if that is indeed what you find. Please let us know if you find it's off and/or adjusting it helps. I suppose since when cold the ECM has to just take a fixed adjustment at start-up till it can start reading what the idle actually is, it could be the cause.

Yes my 88 does that when really cold. Also I must let it idle for a while before taking off other wise after I travel 15-20 miles on the freeway and I get off the express way and come to a stop, the computer thinks it hasnt completed the cycle and when I am waiting at the light it will rev up to 3k sometimes until the computer feels it has completed its mission. Strange! But if it has ample time to warm up before taking off in the winter it will not do this.

[This message has been edited by solotwo (edited 12-03-2010).]

3000? Scam CTS says 70? Is a bit too high for 70*F normally.

MAT can read all over the place... Idle read 120-170*F normally with engine is hot. Hit the gas and MAT reads about ambient temp. It's not constant by all means like V6.

Check tach again the ECM. Tach = ECM RPM

Check for vac leak when engine is cold. replace PCV valve, it maybe partly stuck when cold.

See if the PROM version... GM has an update to fix some problems. Tho your problem is not listed as fix. I think they are still available. try acdelco part and gmdirect.com
See cave. DIS in L4 engine

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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

My first Fiero ('87 Duke) did the same thing. I just HATED it when it would idle at 3000 RPM when first started. It would be noisy as hell and people would look at me like I was some kind of retard pretending to be Ronnie Roadracer.

So what I did was connect a OFF/ON switch to one of the wires on the IAC valve (sorry, I forget which wire). I would turn the switch OFF before I shut off the engine. This would "disconnect" the electrical control of the IAC valve. Then the next time I started the engine, I would leave this switch OFF for the first minute or so. This would keep the engine idling at whatever the minimum idle speed was the last time the engine was running. After a minute of running I would turn this switch ON and the IAC would then be active. However, the idle speed would not go up to 3000 RPM as the engine had already been running for a minute or so.

I found that this solution worked perfectly, as long as I remembered to always turn the switch OFF before I shut off the engine. It wouldn't set any trouble codes either.

I might also add that my '84 Duke does not have this problem. At startup the idle is perhaps 1600 RPM or thereabouts. No need for one of my custom switches.

[EDIT] Just for fun, I looked up the first time I ever discussed this here... back in April of 1999. Anyway, I discovered much to my chagrin that my memory isn't 100%. Here's what I posted almost 12 years ago. My facts were pretty close, but not perfect.

quote Originally posted by Patrick: With my Fiero, the high idle problem occurred when I restarted the engine after it had already been warmed up. The damn thing would "idle" at 3000-3500 RPM for about a minute. People would look at me like I was some kind of a jerk! Before I found out about these replacement PROMs, I cured this problem by installing a switch on my console that is wired into the Idle Air Control valve on the throttle body. It's the IAC that controls the idle speed, and my switch prevents the IAC from cranking up the idle speed when I don't want it to.

I never did swap out the PROM, but more information on these replacement PROMs (which may actually be relevant to this discussion) can be found in the rest of thread Here. Ogre, you remember this thread, don't you?

[This message has been edited by Patrick (edited 12-04-2010).]

Sorry, when I said jmpering out the ALDL maxes out all the sensors I forgot I was talking to informed car folks, not everyday people. Jumpering out ALDL does move the IAC to it's maximum step and disconnecting it locks it there so minimum air can be st at the lowest idle rpm possible. I know the spec is 500 rpm but not all engines can idle that low so setting it at 600 won't hurt anything (lowest idle possible).

Judging by the post comments I would say the problem can very well come from prom programming. Either that or I have a cold vacuum leak that goes away after 20 seconds (doubtful).

If I get time this weekend I will pull my prom and read it with Tunercat.

quote Originally posted by Patrick: I never did swap out the PROM, but more information on these replacement PROMs (which may actually be relevant to this discussion) can be found in the rest of thread Here. Ogre, you remember this thread, don't you?

I read it.... At that time, I didn't know I had a coolant problem making my engine hot. Coolant problem was fix long ago. I use 195* Tstat and fan is off most time...

Also... I do have the PROM from the TSB. (ATCA broadcast code from Table 2, same TSB in DIS article.) Even tho coolant problem was fix, I had some "Spark knock " in certain condition. PROM update fix that. I got the PROM from http://www.gmpartsdirect.com/ 5 years ago.

And I have notes from my PROM "hack." See cave, 1227748 ECM notes.

quote Originally posted by sportcoupe: Sorry, when I said jmpering out the ALDL maxes out all the sensors I forgot I was talking to informed car folks, not everyday people. Jumpering out ALDL does move the IAC to it's maximum step and disconnecting it locks it there so minimum air can be st at the lowest idle rpm possible. I know the spec is 500 rpm but not all engines can idle that low so setting it at 600 won't hurt anything (lowest idle possible).

ALDL jumper A-B Closes the IAC on 87 & up L4...
Set idle stop for 600 +/- 50 RPM
See cave, Idle Stop.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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

[This message has been edited by theogre (edited 12-04-2010).]

Just to note, my 84 L4 upon cold start would shoot up to 2500 really fast and stay there for some time (maybe up to 30 seconds) Then it would idle down to 2200, then 10-15 seconds later to 2000. When the engine was finally warm, I idled anywhere between 2300 and 2500. I replaced all vacuum lines and the gasket on the air cleaner and throttle body. The cold start idle is now 2200 in the beginning for like 10-15 seconds, then goes down to 1900-2000 for another 15 seconds, and then slowly but smoothly makes it way down to 900-1000 rpm when the engine is sufficiently warm. I am still not satisfied with the cold start idle and may change the air cleaner temp sensor, engine temp sensor, and coolant temp sensor.

I just want to add that my 87 Duke never goes over 2000ish on idle. Ever. Doesn't matter the situation or temperature.

quote Originally posted by faaaaq: I just want to add that my 87 Duke never goes over 2000ish on idle. Ever. Doesn't matter the situation or temperature.

Thanks, that proves that it isn't programed into the prom then.

quote Originally posted by sportcoupe: Thanks, that proves that it isn't programed into the prom then.

???

All that proves is that it may not be programmed into the particular PROM that he's running.

quote Originally posted by Patrick: I never did swap out the PROM, but more information on these replacement PROMs (which may actually be relevant to this discussion) can be found in the rest of thread Here.

quote Originally posted by sportcoupe:My '88 2.5L (5 speed) goes to almost 3000 rpm on a cold start-up then?

That can't be good for the main bearings and stuff with little or no oil pressure for the first couple of seconds.

quote Originally posted by Patrick: ??? All that proves is that it may not be programmed into the particular PROM that he's running.

Yes... There are 10 OE and 4 update PROMs.
My PROM had idle in normal range but I needed the update prom for spark knock.

Also, I reread the TSB and notice:

quote 2) Look for that PROM I.D. in Table 1 or Table 2 as indicated below, and select the corresponding required parts: If the major condition is hard hot engine restart, use Table 1. If hard hot engine restart is not the major problem, but the condition is intermittent high idle (similar to cold fast idle), spark knock, and/or Code 42, use Table 2.

Mean I was wrong above... You likely need an update PROM.

Note... If you have OE ECM label that matches PROM label then see cave, PROM ID in ECM section.

Also... check Bluestreak, know for after market ignition part. They have update prom they say. Maybe cheaper?

Check things above first. If engine is good then get an update PROM. (TSB table 2)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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

Update 1-18-11

I finally got around to pulling the PROM and reading it. I was successful in reading it with my programmer and saved it to my laptop. I then edited the BIN table "IAC Warm Park Position Vs. Coolant Temp". I also lowered my fan turn on temp by 15°F while I was in there.

I erased the stock PROM and re-programmed it with my edited BIN and started the Fiero. My cold start rpm is now 1500 rpm. MUCH better then the old 3000 rpm on cold startup. Now maybe people won't stare so much in parking lots. LOL.

Good

If you need a lower fan turn on then likely have a coolant system with a problem or 2...
87-88 L4 should not use the fan except running engine w/ long idle time. If car is moving at all then fan should be off.
even with 100*F, it uses fan very rarely. (I know... my a/c doesn't work and I'm not using a/c control as a rad fan switch.)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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

My 88 Duke does the same thing on cold starts, it jumps up to 2000-2500 and stays there till it warms up and then it idles normally at 1000 RPM. But even when it's cold It drops to 1100-1500 when I put it in reverse (normally followed by a loudish CLUNK. Gotta love when it slams itself into the trunk wall! Or it could be a loose dog bone bolt again.) or drive.

[This message has been edited by mattwa (edited 01-19-2011).]

I have no problem with cooling, especially in wintertime as the fan never runs no matter how long you sit idling. I only lowered the fan turn on temp for two reasons:

1) I had the BIN open for editing and it was very easy.
2) It is my opinion that the engine shouldn't have to be 225°F before fan comes on, that's just too hot (IMO). 210°F is much better.