1988 Chevy Beretta Rough Idle

tobester

Does anybody know of a good place to start diagnosing a rough idle on a 1988 Chevy Beretta GT)? Has the 2.8L V6 engine. It also 'hunts" alot with the rpm varying from 450 rpm to as high as 1500 rpm when it surges. I have access to a OTC diagnostic tool, just don't know the best place to start looking. Any help would be appreciated.

Thanks

alcan

Has the battery been disconnected or run down requiring a boost recently?

tobester

No, I have not had to disconnect the battery or boost it in well over a year. It is always worse as the engine wrms up (20 minutes of driving or more). I guess I'll just bite the bullet and start checking things (compression, sensors, etc).

rktman

How rough - to the point of affecting driveability? Had an '88 for years and the biggest culprit in the idle department was faulty ignition coils. There are three of them as you know. You may want to check for proper spark there. They're in an awkward location, but you can service them yourself.

tboner1965

TB

dvr2

I have a 1990 V6 3.1L and I have exactly the same problem. I recently had to replace an alternator twice in the course of one month, so my battery was run down almost completely twice before. How can the latter affect engine's idle run? Thanks a lot!

tobester

Thanks for the tip on the vacuum leak. Hadn't thought about it but after 12 years, that rubber starts to get brittle. To answer rktman question, it isn't rough enough to affect driveability, but it's the combination of the rough idle and hunting that bothers me. I'm going to try and take a look at this weekend. I changed the ignition coils about a year ago when the car died on me. It ended up being the crank sensor, but I wonder if there is any difference between the Delco Ignition coils and the aftermarket that I put in?

jgmilberg

If you replace the coil packs you are supposed to replace the ignition module that they bolt on to. If you get a bad coil it will kill the module, and vice versa. Take them off and in to your local auto parts store to have them tested. Have you checked or changed the oxygen sensor? If you have access to the scan tool then hook it up and check the o2 sensor values. If they do not jump around erratically the sensor is bad. It will not set a trouble code or turn the check engine light on. This will cause a rich condition that will load up your plugs and cause the rise/fall condition in your idle.

tobester

John, I did replace the module at the same time I replaced the coils. I do access to a scan tool, so I'll check the oxygen sensor tonight.

Thanks

chevyrog1

hi

a faulty charging system can affect idle in several ways
if the coil is not receiving the proper incoming voltage then it can not properly generate sparkplug voltage consistently
Also if the charging system is malfunctioning it can also affect sensor operation, which can affect pcm functions etc etc. This also can lead to effects in transaxle/transmission function.
hope this helps answer your question

Mr_Shiftright

Computers really don't like voltage drops!