Thread: 1500 rpm cut out or misfire

So my girlfriend just got a 97 GP GT and it seems like it was misfiring all the time when cruising at 1500 rpms (it just keeps sputtering and bucking), and then it would do it again at WOT at 3k and 4k rpms. It also has a tough time trying to find idle speed after letting off the gas, but this isn't really that noticable. I just changed the wires and plugs, which revealed rust on the coil packs on the number 5 and 6 wire connections. I sanded those connections and everything seemed great, I also took off the TB and cleaned it completely and removed the MAF grill, just to make sure air flow was okay, but still it cuts out when cruising at 1500 rpms. Any ideas on what this could be? Ignition? Fuel delivery or fuel itself (I've used BP 87 the past 2 and only fill ups since she got the car)? Sensors not doing thier job? I was thinking it would be the MAF but is there a way to test if it's bad? Any insight is greatly appreciated. I'm tired of having to drive at 2000 rpms or 1000, becuase I can't driving in between. If anyone's from the Cleveland Ohio area maybe we could meet up so I could get a second point of view on this problem since it's sometimes hard describing problems in words.

Edit: I unplugged the MAF and have driven about 25 miles and the 1500 rpm cut out is a lot better, but idle sucks, especially on a cold start. And by sucks I mean the car is going crazy and reving anywhere between 400-1200 rpms, but once the engine is warmed up, the idle seems okay. Any ideas? How are the o2 sensors on these cars? Should I try replacing those before I go searching for a MAF?

Edit: 9-11 (2:11am)

I dont know....MAF are pretty common to go out on our cars.If you unplugged it and it ran better, I would start there. Have you looked at the IAC yet or the ICM? I would look there and see what happens. Do you get any codes or anything when all of this happens? does the vehicle idle OK without giving it any gas, or does giving it gas smooth it out? When you get on it, does it run good in the upper RPM range? Have you tried getting gas from somewhere else? Do you have a way to scan the vehicle to see what is actually happening?

I had the MAF unplugged today when I drove it around and it idled like garbage, and on cold start it would rev between 400-2500 rpms without me even touching the gas, so the MAF should be fine. I plugged it back in and the initial 1500 rpm problem came back though. My friend just picked me up a front o2 sensor, so that should help the problem a little or completely. In upper rpms it runs fine. Fluid power throughout the powerband if it's above 2000. She's only had the car for about 3 weeks so I haven't been able to try different gas yet, but the only 2 fill ups were from BP 87 (My GTI only likes BP 93 so I thought i'd stay with them). We are both away at school now so my tools and such aren't always handy until weekends I head home, but I do have access to my friends scanner. I'm first going to replace the o2 sensors and take it from there. I also want to clean the MAF better than I did before just to make sure. As for the IAC, when I cleaned the TB it seemed fine and seemed like it was working properly, but I might keep an eye on that as well. No codes yet, other than the MAF being unplugged, so the car really isn't making this an easy diagnosis. Thanks for the input though. I'll keep updating as I keep trying new things.

Originally Posted by s7falcon

I have a 97 - same engine - very similar problem - at 1500rpms i get the slight hesitatation or kinda like a chuggling ..but start up, idling, accelleration, high r's all good...it is very specific and consistent..I'm gona try cleaning the fuel injectors maybe this weekend...please please keep any progress posted ..and I will do the same..if anyone has corrected this let us know..post or email me at s7falcon@yahoo.com or call my cell 203 520 3003 (Connecticut) anytime!!

Sounds exactly like my problem. I'll keep you posted if I figure anything about. I'm also going to be cleaning the fuel injectors when I replace the front o2 sensor. Good to hear I'm not the only one having this problem since it seems really weird to me how consistant it is and only at spot in the powerband.

As an update, i was driving the car around as much as possible just trying to make it run funky hoping that the SES light would come on and actually tell me something, sure enough, after about 15 miles of 1500rpm driving, boom, SES comes on. So now I'm headed to Autozone to get it scanned (of course I would not bring mine with me to college, bad choice), which will hopefully give some guidance to this search. I'll keep you posted.

Apologies for posting so many times, but I hope whomever is reading this can get some guidance out of it. So I took the car to Ricerzone and had them scan it, and 3 codes came up. p0171 p0122 p0102

-One was for the MAF having low input (I had it unplugged just 2 days before, so that one's off the list for now)
-Second was for the TPS (throttle positioning sensor) haven't ruled this one out yet, but being that I just had the TB off the car to clean it I suspect that unplugging it and having the eye turned to the first click triggered this code also.
-Third, i'm not doing the codes in order, sorry. was for engine running lean in bank 1, which i sould assume is the front bank.

After looking on here for the codes i found multiple writeups saying that the lean mixture code is due to a vaccum leak, o2 sensor, or MAF, or a combination of the 3. As mentioned before, I do have the front o2 sensor at home but can't get it installed till next week, at that time I will also check for vaccum leaks with carb cleaner and see where that takes me. Finally I will be cleaning the MAF yet again to ensure that it is still working properly. Hopefully that will fix this problem. Hope this helps someone, any more input is greatly appreciated.

S7falcon... yes there are 2 o2 sensors on the GP. The main one is right behind the rear cylinder bank on the exhaust manifold right it goes to the downpipe, then there's another one, IMO less important since you can run without it, right after the Cat converter and before the resontator on what's called the U-bend. The one I got is the front one since it controls the most A/F ratio settings. Does your car seem to die for a quick second when you let off the gas at all? I just noticed my GF's did yesterday and that could also point to a vaccum leak.

did you look into cleaning the IAC either?

Yeah, took it off and cleaned it competely when i cleaned the TB.

anyone?

I'm heading home tonight and will be working on the car tonight and tomorrow so I'll update with any details, but yeah anyone else have this problem or insight?

Alright, so here's the update. After working on the car all weekend I do have some results to post. I went ahead and replaced the coilpacks with GTP ones (10,000 volts more baby!!!!) and I did notice that the center coil that I removed was not a standard ACDelco like the others, but after driving around for a while... problem still existed, but the car did have a little more confidence. Then, one of my friends from GPONA came over and we replaced the O2 sensor with a NTK one, and the old sensor was completely white (so the car was running very very lean) and just in bad shape. After replacing that, the car idled like garbage and stalled out multiple times but I drove it about 50 miles hoping that the fuel trims would finally adjust to the new o2 sensor, but still nothing. So, the next day I pulled the MAF and cleaned it extremly well and checked the IAC again, but this time the car ran terrible again unless I unplugged the MAF, then it ran great. So I drove the car around with the MAF unplugged for a while, but the 1500 rpm problem was still there. So I stopped at BP and put 3/4 a tank of 93 gas in the tank and 1/2 bottle of seafoam and then seafoamed the car through the vaccum line when I got home. There weren't really any results at first and I had seafoamed the car 2 weeks earlier with no success, but when I drove the car up to college today, 65 mile trip, the car ran great. All the troubles are gone and for no it seems to be just fine. I'm putting my money on the 93 plus seafoam in the gastank. I'm going to run the run this tank to E and then fill up with 87 again and see what happens, but as of now it seems as though a fuel problem must have been the culprit, or that the changes I made over the weekend just took really long to adjust themselves. As usual, I'll update if anything else happens or I get any more information.

I haven't been able to drive the car today, so I'm not sure if the problem is going to come back yet, but yesterday and it seemed fine but I replaced and cleaned a lot as mentioned in my last post last night so I don't know what actually contributed to it working, but it could just be a fluck and the problem might come back. As for the motor mounts, I'm not sure. I do have the upper front (dog bone) motor mounts flipped but that didn't solve anything I just did it for a little more response of torque, as for the the lower motor mount I have no idea what kind of shape its in, but I can't quite see how that would cause an rpm problem, other than getting on the throttle hard and the engine rocking or bucking around. But yes, Ed Morad is a pretty cool guy from what I hear and the one time I ordered a part from him it was at my door in a day, but then again I do live in Cleveland right down the street from Ed's place. I highly suggest going to him for parts.