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04 Grand Prix Stuttering on acceleration

N

NewtoGP

New member
Hello,

In need of some assistance here on a problem I cannot seem to find a good search result for online.

Symptoms: From 1/4 to 3/4 throttle and inconsistently based on the current RPM's / Gear my car is stuttering / losing almost all power. This happens at all speeds, is particularly apparent on acceleration. Thought it was the TPS, then found out I have a Drive by wire throttle body.... It has only happened once from a stop that when I was accelerating I gave it gas and the car basically just idled and didn't go anywhere till I pumped the throttle or got it above the 3/4 throttle mark. Power under all other conditions except for when this happens feels appropriate, it idles fine and runs great for all other intents and purposes - burns about a quart of oil between changes and the engine has just hit 100k.

What I have done thus far: Originally thought it was the tranny because of how it felt on shifting - tranny shop of course agreed and thank GOD it was under warranty and the warranty company never came out to inspect the transmission - they rebuilt it - which did nothing to alleviate the symptoms. I am throwing a code for the O2 sensor, it doesn't code for anything else other than the ABS which is also thanks to the stinking tranny shop not feeding the wires for the wheel speed sensor correctly.... (They also left a control arm completely unattached... and now the front end of my car makes horrible clunking sounds when going over bumps even though I reattached it - that will be for another thread in the future I suppose.) I bought a used throttle body on ebay since you can't just buy that control module that is attached to the throttle body. The problem MAY be a tiny bit worse with the other throttle body on now but the difference is very small.

My next steps are to go to a pick a part and get another throttle body as everything I have researched says this is a TPS issue... and apparently that is a part of the whole throttle body system.

Any and all help is MUCH appreciated!

Thank you.
 


control arm?...did you mean end links?

Did you check for vac leaks, plug wires, cracked ignition coils?
Maybe check out that O2 sensor.
 
The MAF is the honeycomb looking part that is between the Air cleaner box and the throttle body itself right? What do you have to do to clean this - mine appeared spotless. Yes I meant end links - wasn't sure of the name of the part but figured you might know what I was referencing. I went a pick a part today to try and get another throttle body assembly - good luck with that when they barely have 03 model anything at the only 2 I could find in town /sigh. Where else could I get one of these besides the typical parts stores.
 


Cat clogged? I've been in a cat clogged vehicle before, accelerated slower than a school bus - literally had one pass us from a light lol (5.7L no less). If it was a clogged CAT, full throttle wouldn't help right and it would be an all over power loss not just at certain Speeds / Rpm's and throttle points. I am asking here, as I do not know but that seemed to make sense to me.
 
MY 02 grand prix has a plugged cat and it souds almost identical to your problem. power fluxuates and is occasionaly very dificult to get up to speed/shifting strange. the other problem with that could be that your plenum is starting to go. the burning of coolant is what plugged my cat.
 
Going to necro this thread as my issue remains. If I unplug the MAF sensor, the car runs great but wants to make me pass out from running super rich - no acceleration issues at all though there is some valve knocking (all normal i imagine). I know there is a chance the new MAF sensor I bought could be defective but discounting that what else could be the issue? Stuttering happens at around 2k - 2750 RPM's, 1/3rd throttle on light acceleration. Once you hit that spot where the car stutters, it continues until you either give it a lot of gas or get up to speed. During acceleration it surges. Also, if I am aggressive with my acceleration instead of being a typical driver, the surging and stuttering are not noticeable.
 
Valve knocking? Does it sound like a bunch of marbles being shook in a can? That would be spark knock.

I beleive that if you have a clogged cat and unplug the MAF the car will run better. Someone else will input if that is true... so it seems to still be pointing to a bad cat. Look under the car inmediatly after driving it at night. If the cat is glowing hot this is a sure sign its clogged
 


I have a situation a little bit like yours. I had a coil go bad. it didnt go all at once... lower RPM is where i noticed it and the more RPM i gave it the more it worked until one day it quit completely.
 
Had a very similar problem to this and it kept getting worse and worse. Turns out it was a clogged cat.
 
Update: I checked the CAT's on it and they seem to be working in good order. Exhaust is hot - bought a laser temp gauge and the front is pushing 550+ degrees at around 2k rpms, the rear is pushing about 400 on the in and on the outlet. I am under the impression that it should be at least a little hotter on the outlet, but that if the CAT is bad the temperature difference is usually about a hundred degrees lower on the outlet.
 
Sorry no, front CAT is 550 on the outlet, rear CAT is 400 on the inlet and outlet (in other words it doesn't seem to be getting any hotter in the 2nd CAT, but also not any cooler.)
 
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That makes sense, it seemed mighty thin to be a CAT but could've sworn I read somewhere that this car had 2 lol... I guess I have 2 steps left, go back to AutoZone and get another MAF for it and if that doesn't fix it and no other thoughts on here, take it in for diagnosis.
 
I am still having issues with my GP, and have bought a bluetooth scan tool to work with the Torque app on my android. I am not sure what I should be looking for to help diagnose this issue. Upstream O2 sensor is switching back and forth as it should, downstream stays pretty steady most of the time at about .75 volts though it does switch during acceleration. If the car bogs on acceleration they both drop to 0 to .1 volts. I checked Knock Retard and from what I have searched it seems excessively high especially when the car bogs and have seen up to 12 degrees of KR, though on non-bog acceleration it hits about 6 degrees.

If none of that is helpful, I can look at other things but need a direction.

Thank you for your assistance!
 
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