• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

RE: CES Light Rough Idle

P

pbxcomm

New member
RE: CES Light Rough Idle

Hello all...
Problem 2003 Grand Prix GT 3.8..
Within the past week of driving, I've noticed a stall when the engine returns to idle. If I increase throttle to around 1500 to 200 RPM then quickly return to idle the engine will stall down to about 100 to 200 RPM then back up to normal idle. It dose this constantly, but more frequent after a long drive.
Now, there are codes "DTC P0300 Engine Misfire Detected - ECU $10" and "P0302 Cylinder 2 Misfire Detected - ECU $10", this is according to what I found in Palmer ScanXL Pro.

Maybe a bad gas cap? Would this cause a misfire on one Cylinder? I've been trying to come up with a solution based on these two issues are related (Stall and now new codes)..

I can clearly hear the misfire at the rear of the car but can't determine which side the misfire is on (seems to be coming from both pipes).

I've recently replace plugs (Iridium's) and wires (GM OEM).

Thoughts?
 


Re: CES Light Rough Idle

Well cylinder 2 is the first cylinder on the back side of the motor closest to the coolant tank on the strut tower.

Personally is it was my car I would swap the coil pack with cylinder 2 on it to a different one, then see if the misfire goes to a different cylinder. It also wouldnt be a bad idea to pull that spark plug and make sure it's not cracked.

As for the idle, I would remove the throttle body from the vehicle and clean it. I bet it's all black the IAC passage is full of crap that needs to be cleaned out if you have never done this. Remove the IAC sensor and MAF before cleaning, the tps sensor can stay in.


Doing these first and help alot in further trying to figure out what may be an issue.
 
Re: CES Light Rough Idle

Well P0300 is random misfires and P0302 is specifically cylinder 2. I wonder if the car threw a P0300 and then narrowed it down to just cylinder 2. Or if it started with P0302 and then found more misfiring.

Misfiring will probably be heard in both pipes since these cars aren't 'true duels' meaning both manifolds meet right in the back of the engine to a single pipe out the back to the split before the mufflers
 
Re: CES Light Rough Idle

Interesting..
I pulled the connector off the MAF.. The idle issue (stalling) seemed to clear itself, but I think I need to drive the vehicle at least another 5 to 10 miles to confirm this. But so far so good.. After I pulled the connector I cleared the codes. I still hear a very slight misfire but not noticeable if you didn't know the vehicle well. There are no more codes, but I'm going to take the vehicle out on the highway to test.. Thanks for the replies, I'll be back..
 
Re: CES Light Rough Idle

Ok... The engine threw another code which I expected due to the MAF was offline.. But I looked back at the history of misfires in the last few months, I have random misfire data on CYL's 1, 2 and 6.. Most misfires on CYL. 2. I'm going to replace all the plugs. If I have any other misfires after the plug replacement, I'll begin with the coil pack swap.
Any recommendations on which spark plugs? Iridium's? I've read much here about which plugs should go in. Perhaps Iridium's aren't the plug of choice any longer?

Thanks again..
 


Re: CES Light Rough Idle

I didn't mention, I did clean the MAF with MAF cleaner back when the stalling started.. No change.
 
Re: CES Light Rough Idle

Hello all..
Could use some more help..
The short version:
No more codes.
Engine seems to have a very slight rhythmic miss, hardly noticeable unless your ear is near the exhaust.. Maybe not a miss at all. Otherwise smooth running at all throttle ranges.
Exception (main problem): Raising the idle to around 1200 to 1300 RPM and quickly returning back to idle, the engine stalls and sometimes quits, never throws a code when it does that.
Here's what I have done as maintenance and my attempt to eliminate the stall:
Spark plug change, Iridium's. The plugs have about 10,000 Mi. on them
Spark Plug Wire change (done at the same time the plugs were changed). GM OEM Premium wire sets.
Fuel Filter. GM (OEM)
Fuel pressure check. From Idle to 4000 RPM = 42 to 45 LBS. steady.
I Tank of Seafoam. 1 OZ to each Gallon)
New Thermostat. GM OEM 195 degree
New Water Pump
New Radiator (needed one anyway)
Temp. ranges right around 200 to 210 degrees
New PCV Valve. GM OEM
I've disconnected the MAF - No change/still stalls/perhaps worse. Palmer ScanXL Pro is not indicating a faulty MAF. The range is from 0.6 LB/MIN to 3.9 LB/MIN (Real time).
I have not used carb spray to check for vacuum leaks, although vacuum is -19 Hg (-64kpa) average on a 60 Mile drive.
So, summary.. When the engine stalls whether the RPM/Engine recovers or stops, there are never any codes thrown.

I'm running out of ideas and I'm not a parts swapper..

Any help/suggestions obviously very much appreciated.
 
Re: CES Light Rough Idle

Might want to check for vac leaks anyway, and maybe check the IAC valve. Did the PCV have new o-rings and the spring on it when it went back in?
 


Re: CES Light Rough Idle

Maybe not your problem, but I had a misfire on cylinder 2......ended up being the #2 fuel injector on mine....maybe something to consider if you exhausted the coil pack ..plugs and wires ..maf...cleaning throttle body etc.
 
You must log in or register to reply here.
Back
Top