Thread: 98 Grand Prix GTP 3800 II, Troubleshooting Rough Idle and Sluggish Acceleration :(

ok i will go to auto zone and borrow the fuel pressure tester and check it. What should the pressure be?

Courtesy of BillBoost:

"Key on 45 is about normal. FSM says 48-52, but that's not typical with miles."

Try searching the site for what the running pressure should be. I'm not 100% sure what that should be.

ok with the key on and engine not started it goes to 45 psi and slowly drops to 35. it takes about 1 minute. With the car started in park at idle it stays at 45. When reving engine up it goes to 55 and stays. So i think the fuel pressure is good. I did order new injectors and new coil packs so hope that will pan everything out when they get here. I never had the time last night to set the gap on the plugs back at.055 but i will do it tonight or tomarrow when im off work. hope that changes things. I did the fuel pressure test when the car was cold. After i drive it for a bit i will do it again when the engine is hot and see if the pressure is the same. as for all the fuel related items that have been replaced, Fuel Pump, Fuel Filter, Fuel Pressure Regulator, Low Speed Fuel Pump Relay, High Speed Fuel Pump Relay, and thats it. Once i get the injectors i will tear the engine down and replace the upper and lower intake manifold gaskets, valve cover gaskets, and the injectors. Those parts wont be here for a few more days tho, Is there anything else that is should try in the mean time, Oh yeah i also ordered a new MAP sensor and Evap Sensor that should come around the same time. I just to keep replacing things to rule them out.

My hole car will be under warranty soon LOL

Thanks

Lol, no kidding. At least you will know that everything is good. You did order the aluminum LIM gaskets, right? It would be a waste to put the plastic ones back in there at this point.

I'm not sure what else there could be. Once you get the plugs back to the proper gap see what you get. That FP seems good so I'd rule out a fuel issue.

I have not i know i have to remove the head light and washer fluid resivor to get to it. By bypass do you mean unpluging it or jumping wires from certain pins. That and the injectors are the only fuel related items that have yet to be replaced.

Quick update on a workaround that i figured. Was going to best buy about 20 miles away. Started car when motor was cold and drove for 10 minutes and the acceleration started to be slugish, took the car our of d and put it in 3rd and got on it a couple of times, 5 minutes later still in 3rd the car was running good drove for another 10 minutes and no problems. Parked the car went into best buy for 15 mins came back oit startrd the car and it took me 5 minutes just to get the car to stay at idle, finally put in gear drove down the road and the car was bogging down and misfiring while trying to get up to 35 mph took 2 minutes to get to that speed. Put the car in 3rd drive and kept hitting the gas and after 5 minutes of surging everything was fine again. Drove 20 miles back to my house with no problems, mabye just a tad bit of slower acceleration. Got back to my house shut the car off and started it immediatly back up with no idle problems, went inside and came back out 5 minutes later and started the car and could barely get it to stay idling. So what I learned is that if i keep the car in 3 rd driving at 55mph the car seems fine, if i shut it off and turn it back on it runs fine. If i shut it off and start it 5 minutes later it does not want to idle or accelerate. Not sure if putting the car in3 rd is doing anything that helps or not. Sorry for the long post just want to be thourogh on exactly what is happening in hopes of getting a diagnosis of the issue.

Ok never mind i found the steps to bypass the resistor i will drive the car tomarrow and get it warm shut it off for 5 minutes and then bypass the resistor and see what happens.

Ok i tried both bypass methods and the problem remains, did the wire bridging and the pin 85 bent out. Tgis did not change anything. Any other ideas?

Ok swaped the gap back to .55 took it for a test drive and it woykd misfire bad when boost hits. It threw an engine code of p1133 front ho2 sensor 1 bank 1 so i hookes up the reader and was watching the sensor data and the #1 o2 sensor was going from .955 to .035 speratically while the 2 nd o2 sensor was remaining fairly consistent. So i putchased new or sensor and was scanning the car on the way back and the sensor is now remaining fairly consistent. I am still going to swap it out and i will post the results. Oh i did clear the code before i went to get the part and drove 10 miles and the code has yet to come back.

Ok replaced the o2 sensor and set the gap on the plugs back at .055 and the car is doing the exact thing besides while accelerating with no boost seems ok but as soon as the boost starts it begins to misfire, like bad plugs. It seems to do this when the car is cold or hot. So not sure of the gap issue, i am going to put it back at .040 and see what that does. Next item to get is a big ass sledge hammer and start from the front of the car and work my way back, and see what that does..... Lol

Hete are some pics of the sensor data not sure if this helps, let me know what i should try to look for

I put a CAi and replaced all the coil packs on the car and now its running different. Driving for 30 mins it runs perfect no issues at all. the MPG Goes to 26 it has never been that high before. So looks like im getting closer to getting this car fixed. It is still doing the idle issue only when you shut it off for 5-10 minutes after driving it for a while and still bogging down only after sitting for a little bit after engine is warm. When the car is cold it runs great. I do still have the plugs gaped at .035 so i will put the gap back at .055 later tonight and see if it still misfires when hitting boost. I will also replace the map sensor tonight. My evap Purge valve will be here in a few days so i will replace that too. the car did throw another code P0440 Evaporative Emission Control Systems. Hope its the evap valve thats having trouble. i did get a loging program on my palm pilot just having issues locating the log to view from the computer. Hope soon i will be able to do full system logs. Just wanted to update you guys on the progress.

i tore the top of the motor down and replaced the lower intake manifold gasket, the plentum gasket, throttle body gasket (again), new 180 tstat with new gasket and orings, new injectors, valve cover gaskets, and put the 3.4 pulley on. Gaped the plugs autolite 606's to .055 took it for a test drive and its running great drove for 30 mins and it was still running great shut it off and started it back up 10 mins later and it started and died, started it up again surged 2 times and paned its self out without touching the throttle. So i am not getting misfire anymore with the plugs gaped at .055 still some trouble with the starting after car is warm but not as near bad as it was. I am going to pick up some ngk tr55 plugs tomarrow and play with some gap ranges and see what i can come up with. Just thaughr i would share the good news with you guys, all the sluggishness and sputtering is gone. Just a little idle issue left. The idle in park warm is at 760ish not sure if thats normal. So glad to get some good results after the amoumt of money ive been dumping into this car.

Nope, everything looked great besides the gaskets, drove it alot today and noticed that if i sat idling for 5 minutes it would give me issues trying to accelerate. Like it was drowning the plugs. I need to get the car tuned, trying to find someone in my area that wants to make some extra money. I live in north west florida, i dont mind driving to somewhere to get some help tuning with some one who knows what they are doing. Any one around the pensacola area that has the tools to tune?

Finally got my car fixed. Turns out that the maf sensor was having trouble when it got warm, not sure what messed it up was only 2 months old. I replaced that guy and everything works perfect. Just to let you guys know how i finally figures it out did the voltmeter test good connections htz would change as throttle changed, so all that checked out. Hooked to obd reader and the maf sensor was streaming data fine. Did both these tests when the car was cold and hot and same results. So after i got the car hot and let it sit for 15 minutes i started it and it died, did this about 20 times. Slowly started wiggling all the connectors and pushing the wires and sensors and tried starting again and same thing. So i then started unhooking each sensor at a time and unpluged the maf sensor and it started and idled fine the first crank. Plugged the maf sensor back in started it and it started and died did this about 10 more times. Unplugged the maf and it srarted perfect. Started the car with the maf unpluged and while the car was idling i plugged the maf in and the car died. Left the car alone and let everything cool, started the car when it was cold and it started perfect. Shut the car off and pulled the maf out and used a heat gun to heat it to 150f and stuck it back on the car hooked it up and started the car and it died, unhooked it and it started perfect. Decided to go buy new maf hooked it in and have not had a single problem for 2 days of driving. Not sure what killed the maf but when it was hot it was a trouble maker, car never threw a ses code about maf. Just wanted to post how i figured this out hope that someone else who runs into this problem will follow the steps and get their car running good too. I want to thank everyone that gave ideas and helped me get my car working again. I need to start new topic on abs light and tracton control lights, its never worked since ive owned the car and thaught i will start trying to tackle another problem.

On the ABS/Trac Off light, you probably have a bad wheel speed sensor which is part of the entire hub assembly and not replaceable w/o changing the whole hub/bearing out. Get it scanned to see which wheel it is and replace the wheel bearing on that side. I'd bet the ABS/Trac light will stay out then. I have the same issue on my GT right now.

If this is the case, go with a Timkin replacement as they seem to be the best on these cars.