Diagnosis help? - Long, technical, and complicated...

[gmrulz4u]

I can't seem to figure out what exactly is causing some problems with my 89 Cutlass(2.8)...I was hoping someone may be able to help.

 

The "main" symptom is poor acceleration and performance in general. I can't think of many things that HAVEN'T been changed.

 

I recently had a COMPLETE tune-up, including every single ignition related component, so I know it's not ignition related at all. I know it's not the EGR valve, and I know it's not an exhaust restriction, such as a cat. converter. Almost everything is brand-new or at least less than 1 year old.

 

Anyways, I have a few clues as to what the problem "may" be.

 

I was off on Monday and had a LOT of driving to do and errands to run, so my engine got very hot, and pretty much stayed hot for the entire day. The cooling system works extremely well, and everything functions as should, so that's not a concern at all.

 

BUT, after the engine was REALLY hot, staying over 200 degrees, every time I would re-start the engine, it would start fine, and then all of a sudden the idle would SHOOT up to about 2500 RPMs. I would just think "whatever" and start to drive anyways. But now, the engine would really "bog down" and feel like it was JUST about to stall whenever I put my foot on the gas/throttle. It would only do it for a SPLIT-SECOND, just like the first 0.5 seconds of gas/throttle. It would eventually go away after the engine was running for a couple minutes...

 

I read something quite interesting about the 2.8 and 3.1 engine, found here:

 

http://www.sts.sae.org/membersonly/techinfo/articles/article6.htm

 

Basically in a nutshell, it states that these engines ECM's rely on the IAC Valve "counts" and position in order to determine the correct A/F ratio whenever the throttle angle percentage is 2% or less. It also states this:

 

Stalling due to undesired IAC valve extension may also occur on start up after the vehicle is shut down when hot. High soak temperatures can cause unintended valve extension.

 

I cleaned the IAC completey the other day, and it hasn't made any difference at all. It did seem and feel kinda "out of shape" though?

 

Anyways, moving on to other clues:

 

My engine has been running rich for what seems to be a LONG time. Not so much so that there's black smoke, but enough to notice it at the gas pump.

 

I also get a lot of data by using my OBD Scanner. For example, I can see that my ECM is try to take away fuel at all times(by lowering the injector on-time), but for some reason it does this most drastically when I am decelerating with my foot off the gas. I know when this occurs, lets say I'm doing 40 MPH and let off the gas completely because I see a red light up ahead, that the engine vacuum goes WAY up. So I thought it might have meant that my engine was "sucking in" fuel from the fuel pressure regulator. But I checked the vacuum hose for the regulator and there was no sign of gasoline at all, it was completely dry.

 

I also noticed that once the engine is really hot, the ECM commands a very low IAC "count", usually going to "0". Meaning that for some reason the ECM doesn't need the IAC to let any air in to maintain it's desired idle, which is usually between 600-700 RPMs.

 

I checked vacuum with my vacuum gauge and it was 18" hg at idle, which is good. The MAP Sensor is working perfectly, and there's no signs of any vacuum leak! I'm at a complete loss as to what the hell the problem could be!!?? I might just go out and buy a damn IAC valve to eliminate it as a possibility.

 

Anyone have ANY idea as to what the hell is going on here!???

 

THANKS!

 

PS I don't get any SES light, and never have for that matter:)

[Slade901]

I did not see you mentioning if you have done the idle-relearn.

 

Replacing the IAC would be the first step.

 

Did you clean the Throttle body and the plenum (plenum passage ways) and egr passage ways?

[Robby1870]

Man, that is very strange, I have never heard of something like that. I would buy a new IAC, see if that works, then if that doesnt, get a known working ECM from a scrapyard and see if that fixes it. Honestly, Im stumped, and the IAC counts going to zero is weird to me.

 

Robby

[gmrulz4u]

Thanks guys!

 

I haven't done an idle re-learn yet, I think I will this weekend.

 

Question, do I HAVE to disconnect the battery, or can I just take the ECM fuse out for about a minute? I'm just trying to think if there's another way to do it...

 

In regards to the IAC counts being "0", I think it could be that the actual IAC position is not corresponding with what the ECM "thinks" or "wants" the IAC to do. For example, if the ECM sensed that it was getting TOO much air, it wouldn't be able to tell WHERE it was coming from, even if it was the IAC itself being open to far, so the ECM would keep telling the IAC to close more and more until it eventually was at "0".

 

And yes, the entire throttle body and EGR passeges were cleaned with TB cleaner just 3 weeks ago...

 

That's the annoying thing about OBD I, too few INPUTS versus OUTPUTS. So many scanner parameters are what the ECM "thinks" is happening, not what is actually happening!!

[Robby1870]

I always just disconnect my negative battery cable for like 5 minutes then hook it back up and start it. I guess you could pull the ECM fuse, cuz its the same as disconnecting the battery (or power) from the ECM. Start it, let it idle, put it in drive and hold your foot on the brake for a minute or so or until the idle smooths out after that minute and your good to go

 

Robby

[OldsmoBeast]

I can't seem to figure out what exactly is causing some problems with my 89 Cutlass(2.8)...I was hoping someone may be able to help.

 

The "main" symptom is poor acceleration and performance in general. I can't think of many things that HAVEN'T been changed.

 

I recently had a COMPLETE tune-up, including every single ignition related component, so I know it's not ignition related at all. I know it's not the EGR valve, and I know it's not an exhaust restriction, such as a cat. converter. Almost everything is brand-new or at least less than 1 year old.

 

Anyways, I have a few clues as to what the problem "may" be.

 

I was off on Monday and had a LOT of driving to do and errands to run, so my engine got very hot, and pretty much stayed hot for the entire day. The cooling system works extremely well, and everything functions as should, so that's not a concern at all.

 

BUT, after the engine was REALLY hot, staying over 200 degrees, every time I would re-start the engine, it would start fine, and then all of a sudden the idle would SHOOT up to about 2500 RPMs. I would just think "whatever" and start to drive anyways. But now, the engine would really "bog down" and feel like it was JUST about to stall whenever I put my foot on the gas/throttle. It would only do it for a SPLIT-SECOND, just like the first 0.5 seconds of gas/throttle. It would eventually go away after the engine was running for a couple minutes...

 

I read something quite interesting about the 2.8 and 3.1 engine, found here:

 

http://www.sts.sae.org/membersonly/techinfo/articles/article6.htm

 

Basically in a nutshell, it states that these engines ECM's rely on the IAC Valve "counts" and position in order to determine the correct A/F ratio whenever the throttle angle percentage is 2% or less. It also states this:

 

Stalling due to undesired IAC valve extension may also occur on start up after the vehicle is shut down when hot. High soak temperatures can cause unintended valve extension.

 

I cleaned the IAC completey the other day, and it hasn't made any difference at all. It did seem and feel kinda "out of shape" though?

 

Anyways, moving on to other clues:

 

My engine has been running rich for what seems to be a LONG time. Not so much so that there's black smoke, but enough to notice it at the gas pump.

 

I also get a lot of data by using my OBD Scanner. For example, I can see that my ECM is try to take away fuel at all times(by lowering the injector on-time), but for some reason it does this most drastically when I am decelerating with my foot off the gas. I know when this occurs, lets say I'm doing 40 MPH and let off the gas completely because I see a red light up ahead, that the engine vacuum goes WAY up. So I thought it might have meant that my engine was "sucking in" fuel from the fuel pressure regulator. But I checked the vacuum hose for the regulator and there was no sign of gasoline at all, it was completely dry.

 

I also noticed that once the engine is really hot, the ECM commands a very low IAC "count", usually going to "0". Meaning that for some reason the ECM doesn't need the IAC to let any air in to maintain it's desired idle, which is usually between 600-700 RPMs.

 

I checked vacuum with my vacuum gauge and it was 18" hg at idle, which is good. The MAP Sensor is working perfectly, and there's no signs of any vacuum leak! I'm at a complete loss as to what the hell the problem could be!!?? I might just go out and buy a damn IAC valve to eliminate it as a possibility.

 

Anyone have ANY idea as to what the hell is going on here!???

 

THANKS!

 

PS I don't get any SES light, and never have for that matter:)

 

i had this type of thing happen with my 3.1.....still happens but i got a 180 Tstat so my car doesn't get as hot anymore.....it doesn't idle high anymore but its not right and it gets bad mileage.

[JS91Z34]

This is just a theoretical sugestion but check to see if the inlet duct is collapsing. When that piece gets worn and hot it will become very flexible and soft.

[gmrulz4u]

This is just a theoretical sugestion but check to see if the inlet duct is collapsing. When that piece gets worn and hot it will become very flexible and soft.

 

See, but that's the thing, my ECM makes NO sense! My IAC "counts" will drop to "0" the hotter the engine gets, indicating that for whatever reason my ECM is getting the air from somewhere else. BUT, knowing this, you would assume that you'd be running lean, but that's not the case!!??

 

Whatever...I'm at a loss...