Multiple issues with 2001 GP GT

Where do I start? 2001 GP GT, 3.8 litre v6. Over the past year and a half, I have replaced the cat, plugs, wires, coils, ICM, TPS, IAC, MAF (3 times), removed and cleaned throttle body.

When starting the cold engine, revs up to 1500 rpm and dies. Need to depress accelerator and hold at about 2500 rpm for 30 seconds before it will stay running.

Once running, rpms fluctuate between 700-1000 at idle. If under the hood, can hear what sounds like a hiss coming from the front (belt end) of the engine only when rpm increases to 1000, and hiss stops when idle drops back to 700.

The 3/6 coil is making an audible snapping sound, like a stray spark. No arcing is visible. The car was stumbling/misfiring when accelerating. This is why the coils and ICM was replaced, did not fix the snapping problem.
Stumbling/misfiring is not as bad anymore.

When the rpms fluctuate from 700-1000 at idle, so does the dash lights, running lights and heater blower motor.

A few times now, the rpms have dropped to a point where the car has almost stalled but didn't. However, the radio shut off and the radio clock reset to 12:00.

The only code it throws is a P0440.

Any ideas? Don't want to keep dropping money into it.

Welcome to AF!!

Check the grounds at the engine and battery. I suspect you have a voltage issue caused by bad grounding. Also check for a vacuum leak. It can cause poor idle quality.

Welcome danben!

Have the battery tested at an autoparts store. A dying one can cause some weird problems. Also, there is a vacuum line from the upper intake manifold to the firewall and towards the passenger fender; if broken it could cause some idle problems and hissing noise.

I would like to note that the spout to which that hose and the brake booster hose attaches to seemed to leak a bit on mine. It can be removed by pinching the two tabs on it, it's a bit tricky but some patience does the job. It has an O-ring to seal against the manifold, you might want to replace it; I was in a hurry and just used some RTV sealant to fix it.

Oscar.

The battery was replaced a year ago. This past Saturday I rebuilt the alternator. Resolved nothing. Oddly enough, the engine stumbles and misfires more when the engine is cold. When it reaches normal operating temperature, is still hesitates, stumbles, misfires, and lacks performance just not as severe as when the engine is cold. One mechanic I spoke to suggested the ignition switch may be bad, any thoughts on this?

The battery was replaced a year ago. This past Saturday I rebuilt the alternator. Resolved nothing. Oddly enough, the engine stumbles and misfires more when the engine is cold. When it reaches normal operating temperature, is still hesitates, stumbles, misfires, and lacks performance just not as severe as when the engine is cold. One mechanic I spoke to suggested the ignition switch may be bad, any thoughts on this?
I have a '98 Monte Carlo with a 3.1 that I bought off of someone real cheap because it was running badly like you describe. I changed all the injectors with known clean ones and it fixed it. The car has 198K miles on it. You also have to make sure the spark plug is the one that GM recommends.

The stumble being more noticeable when cold than when hot, would make me think you might have a problem with either a vacuum leak, dirty TB or dirty/failing IAC.

Cold engines need more air/fuel hen cold than when hot. Any of the above conditions could be more apparent when cold.

Oscar.

The stumble being more noticeable when cold than when hot, would make me think you might have a problem with either a vacuum leak, dirty TB or dirty/failing IAC.

Cold engines need more air/fuel hen cold than when hot. Any of the above conditions could be more apparent when cold.

Oscar.

The throttle body was removed and cleaned and the IAC was replaced two weeks ago. I am going to start looking for a vacuum leak.

Update, could not resolve problem throughout Xmas and new years. Put another set of wires on it and new plugs again, no change.

Last night, while under the hood, I could hear a ticking, like a stray spark. I figured there is no way it can be the plugs or wires, they were replaced two weeks ago. Decided to remove the metal caps off the spark plug boots. No more ticking, no more misfire, and no more stumbling on acceleration. RPMs still fluctuate between 700 and 1000 but I can live with that.

Checked the pressure in the fuel rail, it was also fluctuating between 40 - 45 psi. Also seem to be getting a lot of noise from the injectors, is this normal?

Decided to remove the metal caps off the spark plug boots.


You have to explain this one to me.......

After thinking about this for awhile, I realized you were talking about the caps that go on the OUTSIDE of the boots......If this is the case, and the boots were the same size as the original ones replaced, the only think I can think of it carbon tracking.....this is a problem, that goes away for awhile if you just replace the boots OR the wires...it comes back.....if you have carbon tracking, you have to replace both at the same time.....also, were OEM plugs used and gapped correctly?

Hate to say this, but disconnect the MAF sensor and see if the idle improves...if ok, it's the MAF....I know that you have replaced it 3x's, but these aftermarket units will drive you crazy.....

Had a car towed to shop, barely ran....watched data on Tech II and MAF hz all over the place...disconnected it and car 's idle improved....customer had choice of cheap after market, or OEM...took the cheap way out.....right out of the box, it wouldn't even start...disconnected it, and car started....got another one.....ok....until one day later...guy was screaming....said he wasn't going to pay for another tow job.....told him to disconnect the MAF, and he was able to drive it to the shop....ordered an OEM, no problem....

Decided to remove the metal caps off the spark plug boots.


You have to explain this one to me.......

On this GT, there are metal cylinders placed over the spark plug wire boots. The have a spring on the engine end of the cylinder that presses against the block to stop the cylinder from rattling. I assume they are some sort of heat shield. Somehow, they must have been drawing the spark through the boot. This kinda makes sense because there were random missfires from all cylinders. It didn't happen all the time, it was spiratic. Lately it seemed to happen more often when the engine reached normal operating temperature.

Decided to remove the metal caps off the spark plug boots.


You have to explain this one to me.......

After thinking about this for awhile, I realized you were talking about the caps that go on the OUTSIDE of the boots......If this is the case, and the boots were the same size as the original ones replaced, the only think I can think of it carbon tracking.....this is a problem, that goes away for awhile if you just replace the boots OR the wires...it comes back.....if you have carbon tracking, you have to replace both at the same time.....also, were OEM plugs used and gapped correctly?

Hate to say this, but disconnect the MAF sensor and see if the idle improves...if ok, it's the MAF....I know that you have replaced it 3x's, but these aftermarket units will drive you crazy.....

Had a car towed to shop, barely ran....watched data on Tech II and MAF hz all over the place...disconnected it and car 's idle improved....customer had choice of cheap after market, or OEM...took the cheap way out.....right out of the box, it wouldn't even start...disconnected it, and car started....got another one.....ok....until one day later...guy was screaming....said he wasn't going to pay for another tow job.....told him to disconnect the MAF, and he was able to drive it to the shop....ordered an OEM, no problem....


I changed the wires and plugs at the same time 2 weeks ago, it did not improve the random misfires. Pulled the heat shields last night, misfire went away. Drove the car for a half hour last night and to work this morning, misfire hasn't returned. I will disconnect the MAF tonight to see if that corrects the idle issue.