Just Purchased 1988 Coupe - Need Help

[Bonnell]

Hi Everyone,

After 25 years I finally have another Vette (the first was a '73). I have just purchased a beautiful 1988 coupe and I have the following problem:

The car simply stopped idling properly and would stall. The computer was replaced and several things such as the A/C display and the A/C functionality were corrected along with the erratic idle.

The new problem is that the car now wants to idle at 500-550 RPM (it previously idles at 600-700RPM). The dealship technician says that this is the correct setting and the computer (is this the ECM?) adjusts to this RPM no matter what he does. The problem is that it will simply quit sometimes as I let off of the gas to brake to a stop - I can see it fall below 500 then it quits. It starts right back and away I go. The only solution is to keep one foot on the gas and the other on the brake when stopping. It does not always quit but I don't take chances.

The tech simply suggested that I use a can of injector cleaner (he can't get it to run any better) and give it a complete tune up.

I am a quick learner but I am NOT a mechanic.

I really need for this car to run as it is my 'driver'.

Any ideas???? Thanks in advance.

 

[WhalePirot]

A new mechanic? Does he know anything about computer controlled cars? He is putting you off, IMHO.

I doubt your original problem was the ECM (computer); seems the symptoms have not changed.

You either have a bad sensor or one out of adjustment. I don't have specs on the '88 but, while it is true that true ECM controls idle speed, 500 is awfully low. There is a 'catch' in the ECM programming to prevent stalling.

Detergent, pump, gasolines will clean injectors as well as any can of cleaner. I posted such, from a GM research project, some time ago.

I'd demand my old ECM and my money back from that 'technician'.

 

[dmrodco]

I had a similar problem with my wifes eclipse. The probelm was the IAC. WE replaced it then adjusted the idle. there was a covered screw on the front of the throttle body that simply pushes the blades open slightly to get the idle correctly. I havent had to do anything like this on my 87 vette yet. I would think there has to be somthing similar on the TPI systems.BTW IAC is IDLE AIR CONTROL. I know the TPI has one. I think your mechanic is a hack and would check around the local vette club to find someone who knows what the heck he's doing. My 2 cents worth.

 

[Corvette-Pilot]

I had this problem with my 97 Dodge RAM1500 4x4.
But it happened after the check engine light came on.
The engine code was for an oxygen sensor problem.

I ended up pulling them out and blowing them off, put em back in.
The problem went away and has not returned (knock on wood)
Those little buggers were $75 each thru Auto Zone so I didn't want to replace them if I didn't have to !

I had read somewhere ? that the O2 sensors can get that black sooty stuff inside them and thus give the ECM wrong info so the car trys to adjust the fuel mixture settings to the point it wont run.

Might be worth a try. Only costs some time.

You also mentioned getting the AC controls and display to work correctly.
Mine seems to be OK some of the time but it sometimes wont let me change the temp or fan speed (electronic control). Still reads the temp, I can select the various outlet settings. Just the temp &/or fan speed locks me out?

Wondered what you had done to fix yours?

 

[Vettelt193]

IAC sounds correct, but you should not adjust the screw on the throttle body... the computer will adjust it for you... just disconnect the battery before swapping the IAC, so the computer will reset

 

[78SilvAnniv]

Welcome Bonnell,

Welcome to Corvette Action Center, good luck with the problems. Come back often, and keep us updated as to your progress and findings. Your solution could help another member one day.
Heidi

 

[Edmond]

Bonnell,

Can't really tell you much, but if your 'service engine soon' light comes on, you can pull the diagnostic codes yourself instead of paying a mechanic $60+ to hook the car up to a computer.

Under the steering wheel, there is this little port and all you have to do is use a paper clip and jumper the top two ports on the right hand side. The 'service engine soon' light will flash a sequence of numbers and that will give you the code. Post them here and everyone will help out.

This was for my Camry, but the dealer said that if the sensors were to somehow get dirty, that would trigger a trouble code as well.

As for the ECM going bad, I'm very skeptical about that because the ECM is extremely well protected and they usually last the life of the car.

 

[MoeJr]

You can adjust that screw on the throttle body. It is for air around the blade. Sometimes as cars get miles on them there is a carbon formed on the blade and it closes that air gap. By adusting the screw you can get it right. I used to adjust the screw along with the TPS to get the idle where I wanted it on my 87 Grand National which had an adjustable TPS. I have never had a problem doing this with a GM car.

 

[BigRed]

I have the same engine as you and my car used to idle rough at the 400-500 mark and sometimes die.

You could play with the IAC but (Not to step on toes) ADJUST the throttle body, thqats what fixed mine. I now idle at 720-740 Rpm its smooth and purr's.

 

[Bonnell]

Thanks for the reply! I just ordered a Chilton's manual and won't have it until next week. Is there any place on the web that you are aware of that has info on these parts (location, etc.)? If I can find the info, I'll give it a try this weekend. I can't afford to have this thing in the shop - besides, I love it and want to drive it - so I intend to try learning as much as possible so taht I can do routine maintenance. Is it difficult to check and adjust the timing?

I'll look up IAC and see what I can do. I was charged $325 for teh ECM so I hope that he knew what he was doing.


Thanks to all for the replies. This is great!

 

[c4ever]

I would do a complete TPS adjustment along with proper idle adjustment procedure. Relatively simple and can make a world of difference. A tune up never hurts either.

Carlo

 

[Edmond]

Thanks for the reply! I just ordered a Chilton's manual and won't have it until next week. Is there any place on the web that you are aware of that has info on these parts (location, etc.)? If I can find the info, I'll give it a try this weekend. I can't afford to have this thing in the shop - besides, I love it and want to drive it - so I intend to try learning as much as possible so taht I can do routine maintenance. Is it difficult to check and adjust the timing?

I'll look up IAC and see what I can do. I was charged $325 for teh ECM so I hope that he knew what he was doing.


Thanks to all for the replies. This is great!

Wanting to do all your own work is a great attitude to have. IMHO, there are only a few things that can't be done by yourself like mounting/balancing tires but the majority of things can be done at home. You save yourself money and you learn a ton about your own car.

 

[MoeJr]

We'll get ya fixed Bonnell. I unfortunately cannot scan stuff on to the computer but I am sure someone is gonna post exactly what ya need to do so you can tackle that Vette this weekend. Keep us posted.

 

[Bonnell]

Hi Everyone,

Again, thanks to all for the replies. I contacted the saleman at the dealership where I purchased the car and he in turn connected me with one of his Corvette techs. He had me adjust a torx (sp?) screw which apparently used to be called the idle screw. He said that it adjusts the minimum idle setting. Two turns and I was at about 700 RPM and all seems well.

He also gave the same advice about the IAC and throttle body as I have seen here.

Now that all of you have given me a starting point, I'm ready to go!

What a great forum!

J Bonnell

 

[MoeJr]

That be the screw we were telling ya about. Like I said usually I adjust it in conjunction with the TPS so that I don't end up relying too much on the screw for idle. It isn't as much for idle as it is used to set the minimum air rate which u usually adjust with the IAC disconnected. But as long as you have no Service Engine Light and it runs ok I would say u are looking good. Just my .02

 

[omega1940]

Idle Problem

I have had an 88 Conv. 4+3 (transmission) for about 18 months and this is my 3rd Corvette.

I have had a few idle problems over the past 18 months and it has always been the O2 Sensor. They are inexpensive at most auto parts stores (I buy Bosch) and you can install them in 5 minutes. They are on the exhaust manifold, driver's side. Pull the single wire connector off the sensor, screw it out and replace it with the new one. Re-connect the wire and you are in business.
If the car has an older O2 sensor, I would bet this is the problem. If not, the IAC (Idle Air Control) could be bad. You can replace this, but it needs to be reset with a voltmeter.

Good luck.

 

[Heyspike]

Hello All, Brand new here, just bought my first vette Thursday. Already found answers to some of my questions--gotta love the forums!!! I have the same idle problem. Also was going to change pcv valve. Looking for a good oil to run in car, I'll go raead that post.--Thanks--John