1990 Engine Idle Issue

Reply Subscribe

Thread Tools

Search this Thread

Jun 16, 2016 | 02:35 PM

eltoro1990

Thread Starter

4th Gear

Joined: Jun 2016

Posts: 4

Likes: 0

1990 Engine Idle Issue

From time to time the engine idles too low and on a rare occasion too high. Also, when idles too low, the battery gauge is extremely low and builds back up once the car eventually starts. To remedy the problem I have done the following:

- Cleaned the throttle body
- Replaced the alternator
- Reset the computer

Despite this, the problem still remains. Can anyone offer any advise on what the root problem is?

Thanks,
Ryan

Jun 16, 2016 | 06:22 PM

aklim

Team Owner

Joined: Jul 2004

Posts: 28,420

Likes: 3,273

From: Hartford WI

Quote:

Originally Posted by eltoro1990

- Cleaned the throttle body
- Replaced the alternator
- Reset the computer

Define "cleaned the throttle body". Did you take the IAC and the IAC housing off and clean the passages? Did you reinstall with new gaskets?

Why was the alternator replaced? Did you have it tested at a rebuild shop or Autozone? There is a huge difference. 2 places tested my alternators and starters and pronounced them OK. A rebuild shop took them apart and they were not.

Reset the computer. How and why?

Jun 16, 2016 | 07:47 PM

eltoro1990

Thread Starter

4th Gear

Joined: Jun 2016

Posts: 4

Likes: 0

Quote:

Originally Posted by aklim

Good questions. For the throttle body, I gave it a good scrubbing on the inside the butterfly covers, but it wasn't that dirty. That's all I did and I wasn't sure what else could be done in regards to the throttle body.

I replaced the alternator because I thought it could be related to the idle issue. When I would start up the car, on occasion, the car would sputter and then die. When it did this I noticed the battery gauge was reading extremely low. I had the battery tested (which is only three months old) and it read it was 70%. At that point I recharged the batter up to 100% and then three days later tested its power and it read 80%. From this, I concluded that the alternator wasn't recharging the battery. So I replaced the alternator yesterday and I thought all was good, she felt good at first. But then, the issue came back.

As far as the computer reset, I turned my car into the shop and had it looked at for three weeks. All they could come up with was that scrub of the throttle body and reset of the computer. Luckily they didn't charge me because they didn't feel that they truly fixed the problem. Sadly they did not. From these details, what do you recommend?

Thanks,
Ryan

Jun 16, 2016 | 07:58 PM

aklim

Team Owner

Joined: Jul 2004

Posts: 28,420

Likes: 3,273

From: Hartford WI

Quote:

Originally Posted by eltoro1990

You need to do it again. Disconnect the IAC, 2 coolant hoses (good time to do a bypass, use the Torx bit to take the top plate off, Unscrew the IAC, remove the IAC housing. Then you can clean everything. THAT is the through way to do the job. I do that every 3 years because I have the injectors cleaned and tested at that time. If you don't reuse your condoms, don't reuse the paper gaskets.

It could be that when it is dying, the alternator is not able to charge up the system hence the low reading? IDK. I would still have the rebuild shop test it before condemning it and throwing parts at a problem. When I change a battery, I test the alternator and vice versa.

You can't reset the computer and hope it fixes the world. It has a LIMITED learning curve in that it adjusts settings TO A POINT. You have reached a part of the ownership where you have to decide if you want to keep it and keep throwing parts at it or buy a scanner and some simple tools. For now, go to autozone after the cleaning and check what the IAC counts are when everything else but the motor is off and engine in closed loop. Before that, check timing

Jun 16, 2016 | 08:30 PM

aklim

Team Owner

Joined: Jul 2004

Posts: 28,420

Likes: 3,273

From: Hartford WI

Once you have it all cleaned with new gaskets, I can tell you how to use the scanner to check for air leaks and set the minimum air rate. Make sure the timing is right first or we can be chasing our tails all day long. Ask me how I know

Last edited by aklim; Jun 16, 2016 at 08:32 PM.

Jun 16, 2016 | 08:48 PM

eltoro1990

Thread Starter

4th Gear

Joined: Jun 2016

Posts: 4

Likes: 0

Quote:

Originally Posted by aklim

Hey I really appreciate your guidance. I'm a novice when working on my vette. I've only had her for about three years. My Dad gave it to me as a welcome home present coming back from Afghanistan. I've learned a lot in the last three years, but I know there is a hell of a lot more to learn. I have a 1990 polo green convertible that's in really good shape, except for this issue. I've been in a rush, like you said, "throwing parts at it" lately because I am moving to Germany in a couple of weeks and I'm taking her with me. I was trying to solve this issue here before I leave. Now, I'm not so sure because I'm simply running out of time. But I'll give it my best shot!

Thanks again,
Ryan

Jun 16, 2016 | 08:53 PM

aklim

Team Owner

Joined: Jul 2004

Posts: 28,420

Likes: 3,273

From: Hartford WI

If it is warmed up in closed loop with nothing else running but the motor and you hook up the scanner and see what the IAC counts are, it might give you a hint at what is wrong. Your target is 20-30 counts on the IAC. If it is too high, it means the ECM wants more air so it commands it to open up more than your target count. If it is lower, the ECM thinks it has too much air and wants to shut down the "controlled air leak". Higher count, turn the screw in. Lower count, turn the screw out. Rev and re read. If it at 0 and you have turned out the screw as much as you can, you need to chase an air leak in the hoses which is why I told you to change the gaskets.