Hey Guys,

This issue has me stumped and I have tried basically everything I could think of and can't seem to figure this out.

THE CAR: 2001 Grand Prix GT. Completely Stock. 197k miles.


THE PROBLEM: While accelerating with 20-50% throttle, the car has a hesitation. The RPM's bounce around between 1600-2000 and feels like apparent miss. Car does gradually gain speed and once cruising is fine. If you accelerate gradually or WOT, there is no hesitation. I have scanned the car several times and no codes are displayed. Only message displayed is a "Low Emissions Cat" because previous owner put on an aftermarket and not OEM cat.


WHAT I HAVE TRIED:

- New MAF (Swapped with one in Bonneville which I know is good)
- New Plugs 20K miles ago when I bought car.
- New plug wires at 20K ago, also replaced them 2K ago when I checked plugs to see if any were bad. (replaced wires because boots separated from wire). All plugs (NGK TR55's) looked fine.
- New Idle Air Control Valve and Fuel Pressure Regulator (This was to fix a rough and surging idle when started)
- New Fuel Filter

Next thing I was going to try was swapping all the coil packs from my Bonny to see if anything changes. Might also try swapping the Ignition Control Module and the harness which plugs into it.

Any other thoughts or suggestions. I have put about 8k miles on car since this first started so the reliability of car hasn't been affected at all. Still idles, runs and drives like any other higher mileage 3800! :D Just wish to get it corrected since my cars always operate to full potential no matter the age or mileage.

I have read a lot about this issue on Grand Prix forums and nobody has a root cause. I feel this forum is more knowledgeable so hopefully we can fix this.

Thanks!

_________________
Eric

2005 SLE, Greystone Metallic, 152K.

A few mods..

I have had this issue with my Bonneville multiple times. Usually if i keep the pedal in the same spot when it starts hesitating, it will continue missing long enough to cause a check engine light. Then you can pull the code. My bet would be the ignition coil for which ever cylinder it is missing on is your issue.

It sounds like you have already covered all the other common causes, so that would be my best guess. Good luck!

_________________
'04 SLE
Crimson Tintcoat
~125K miles

I would bet theres a good chance its the coils or the module... i would look at that and see, try swaping the bonnies on it and see how it runs..

_________________
1995 se
128,101
custom FWI
rt-95 rims look kinda like crosslaces
6000k hids
f- body muffler dual output
96-99 headlight conversion, clear markers

+2 on coils and/or ICM.

_________________
-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

+3. I chased weird hesitation and misfire issues for 2 years until I replaced my ICM. After replacing the ICM, it was like I had a new car.

_________________
- Greg | -- Project Prasinos -- |

1995 LeSabre Custom: 312K Miles | Custom K&N CAI | Edelbrock SDT Muffler | Camaro Tips | 180 T-stat | LED Interior
& Exterior | 20% Tint | PA Grill & Portholes | Limited Trim | GTP Rims | Ported LIM | Plus Many More Mods | Restoration Thread
2001 Bonneville SSEi: 225K Miles | Instense FWI | Intense MPS (3.4") | 180 T-stat | ZZP Plog | Ported Rear Manifold |
ZZP 3" Downpipe | Magnaflow Cat | Retrofitted HIDs | GenV M90 | GXP Brake Upgrade | 35% Tint | Plus Many More Mods |
2005 Bonneville GXP: 101K Miles | Custom FWI
2009 G8 GT: 89K Miles | 35% Tint | Roto-Fab CAI | SOLO Mach Exhaust | BMR Tunnel Brace | BMR Sub Frames | BMR STB |
Kooks Headers | QTP Electric Cutouts | BMR Sway Bars | Elite Engineering Catch Can | Innovative Dual Wideband Kit
1984 Caprice Classic Wagon: 86K Miles | Restoration Project

Blowing the dust off this one...

Had a chance to work on the car today since it was nice and I got caught up on other projects.

I swapped over the 3 coil packs and the ICM onto the Grand Prix and have the same hesitation. Nothing changed. I did notice this; when I swapped everything over and went for a ride, the car ran fine for 2-3 miles while the car was "cold." Once it warmed up a bit, the hesitation came right back.

Any other suggestions? I'm stumped. Thinking it might be within the ICM harness which connects to the ICM board but I sure hope not. Don't wanna track, replace and re-splice all those wires in.

Thanks!

_________________
Eric

2005 SLE, Greystone Metallic, 152K.

A few mods..