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Rough Idle/ Electrical problems

3635 Views 4 Replies 4 Participants Last post by  jebx
1994 Gmc Sonoma Engin is 1 yr old
When in traffic or at long stop light waits I get a rough idle. The longer the time with no gas applied the rougher it gets. Takes alot longer time to start when in park. RPM gage bounces along with idle. When you apply gas and bring RPM up a lil bit it smouths out until you let off gas. Replaced alot of sensers, plugs, wires, cap/roter, fuel filter, and just about every thing I can think of to no avail. Any one had or heard of this problem before?

Altanator went bad put in new one. While on highway with stereo on, hit turn signal and all gages jerk. While at a stop light you can sea stereo and trun signal in gages. ( RPM and battery gague keeps beat with music, with stereo off RPM and battery gage twitchs with turn signal rithem.) Lose power to stereo alot. Door locks didnt work once after turning off engin. Started back up once it was running hit door locks and it killed motor. I disconnected amp for stereo and seems to be fine now. Any one familar with what probs the amp could cause with the truck?
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· Registered
3,083 Posts
1st problem: Is the new engine the same specs as the old one? If not your TBI computer could be throwing a fit. Is the SES light on? And have you ever cleaned the injectors (pull the air cleaner and with the engine running at idle look at the steam of fuel from the injectors, it should be a a nice cone)

2nd problem: How old is your battery? How big is your alternator? How many watts is your amp? Sounds to me like there isn't enough power to go around, and it could be part of the cause of the 1st prob.


Welcome to GMFS! :bowtie:

· Registered
923 Posts
What you need to do is have it hooked to a scope (Ignition scope) to see exactly what is going on. That would tell you if once cylinder is firing high. I did have a wire/cap/rotor from autozone go out in user a year, cheap crappy parts.

I known issue sometimes is for the distributor magnets to crack. This happened on my '95 350(4.3s do this too) and have a slight miss. It was really annooying, I had new wires, cap, rotor, plugs and still missed a little.

Here is a little info: (the picture shows the extreme, i just had cracking in the magnet, no chunks missing)

What you need to determine is if it's fuel or ignition problem. You could have a bad injectory leaking or dirty and not getting a good spray. Have you had the fuel pressure tested? Is there a check engine light? With running that rough I would think you'd set an oxygen sesnor code for running rich.

I would clean your battery terminals and inspect the body grounds in reagards to your other issue. When I say clean them, pull the cables off the terminals and clean them up good. Clean off any big corrosion chunks and dip them in a cup of water mixed with a little baking soda one at a time (use something you don't care about to dip em in). When you dip them it will foam a little, chemical reaction from the corrosion and the baking soda.
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