I just did my spark plugs and coil packs, all new, ac delco iridiums. For a couple days my car ran perfect...the rpm guage didnt move a hair and it purred like a lion. Now suddenly im getting a rough idle, not the same kind i had before...the car isnt bucking like a misfire the engine just simply sounds like its running like **** going up and down in rpm and sometimes a random vibration.

At the sae time this happens my fuel guage also goes wonky. Normally it sticks at F because its busted but it seems like it goes all over the place whenever im stopped and the rough idle starts. Im not sure if the two are connected. Anyone have any ideas?

Oh its a 2000 Monte Carlo SS with 190k miles. Standard 3.8

 

Did you do the fuel filter yet?

Could be one of the sensors on the TB, could be the fuel filter, and could be the FPR.

Pull the vacuum hose off the FPR and if it is wet or smells like fuel that could be going bad.

 

You would tink if the spark plugs worked for a few days they wouldnt suddenly go bad right? Thats my worst fear. I just did the fuel filter yes, no leaks. Ill look at the fpr and check the MAF again. Also could be the aftermarket coils...they were cheapies.

 

Would a bad alternator cause the wonky guages?

 

If it's just the fuel gauge, I wouldn't think the alternator. You have a voltage gauge on the car, what's that reading :P

 

The reading is fine but when you disconnect the battery the car shuts off. Thats why i was thinking the alt.

 

You can go to any autoparts store and have the alt bench tested if you really suspect it.

I would think you would see a drop from 14 while driving with a bunch of accessories on if the alt was bad.

 

I never trust the gauges on any Chevy I've owned. But I agree.

 

I just went through an issue where I believe the diodes in my alt were causing my battery drain (but all gauges worked fine). It was benched tested numerous times and only failed once. Since I could not secure it as the problem, at the time, I put it in and the next day, it made a foul electrical odor, changed it no issues to date.

But, the alt should not cause the idle problems.

I personally don't have a lot of comfort with aftermarket coils. I trust OEM and used OEM before aftermarket coils. But admittedly, you should get a year or so (or longer) out of them.

Like Chibi mentioned, you can check the fuel regulator and fuel filter. Since you mentioned when this happens your fuel gauge goes nuts, my guess is that you have a possible wiring problem. The harness that sends the fuel level data is probably the same harness that powers the fuel pump. You might have a damaged wire or a intermittent ground. Just a guess.

If the alt was causing this, you'd have a lot of other issues. These cars with a low battery tend to loose their brains.

 

Im gonna test the fuel pressure and alt today before i leave work. I might end up getting one anyway because its making a lot of noise.

Whats the best way to access the wiring to the fuel pump? Do i need to go through the access door?

So far ive replaced the IAC, cleaned the MAF and the TB, replaced the air filter, replaced the fuel filter, replaced spark plugs and coils, still has the same wires on them, and the battery is fairly new. I also put some marvel mystery oil in the gas.