hesitation or hiccup while driving

[gutterjrn]

I have a 99 grand prix gt with 140K miles. when driving there is an occasional hiccup when driving and sometimes even when braking or stopped. It isnt very consistant. When this happens the tach drops 500 rpms or so but the car doesn die. Any ideas on what the likely culprit is? This has been happening for a few days.

My first thought is to change the fuel filter as it hasnt been changed for a few years, other than that I dont have any ideas on where to begin.

Last time any work of any significance was done was at 95K and the things replaced where fuel filter, PCM, fuel injectors, spark plugs, plug wires, .... and so on (the dealership didnt know what the problem was so they started replacing stuff and the true problem ended up being the PCM)

[richtazz]

I would change the fuel filter because it's overdue, but I don't think it's causing your issue. does the ABS/Trac-off lights come on when this happens? If so, then I would suspect a bad crank position sensor. Even if it doesn't, the CKPS is the first thing I would look into.

[gutterjrn]

Thanks....NO lights come on when this happens. I also had the codes checked to see if any existed, there were NO error codes.

[richtazz]

regretfully, the CKPS will not always trip a code when they start to fail. It usually has to get to a point where the car completely stalls before a CKPS code will trip.

[tblake]

Rich, and even then it sometimes wont trip a code (the case with my car).

I wonder if this could be a MAF issues. To the OP, try unplugging the MAF sensor and driving the car like that for a day or two to see if the hesitation goes away.

[gutterjrn]

Is the MAF plug the one on the flex hose just after the air filter? Thanks.

[tblake]

http://www.automotiveforums.com/vbul...d.php?t=746374

Unplug the maf with the car off, and start it. Once it idles down take it for a drive and see if the hesitation is gone. With the MAF unplugged, there will be an SES light, and you might lose a mile or so per gallon, but its ok to drive it like this for a while. I drove mine with my MAF unplugged for a week while I waited for a replacement to arrive.

[tblake]

BTW, when was the last full tune up done on this car?

[gutterjrn]

My last tune up was around 100K, 40K miles ago.

[tblake]

was that when you first started noticing the issue? What brand plugs and wires did you go with?

[gutterjrn]

No, this issue just started. I dont know what brand of plugs the dealership used.

I decided to take it for a little drive today before I unpluged the sensor. I noticed that it only starts to do this once it gets completely warmed up. Tomorrow I am going to unplug the sensor and drive it to work that way to see if anything changes.

[c3d6c4c5d9]

The CKPS is definately a common failure on GP's, I have replaced the one on my 99 GTP at least twice in 90k miles. I have also experienced the fishbite/hiccup/random struggle with my car. In all the GP forums out there, they pretty much all recommend the CKPS, and then usually the fuel filter and eventually the MAF all within good reason. Unfortunately there are posts where an owner will get to the point where they've replaced all of the listed parts with no solution. . .
Bare with me - just recently I finished a top swap on my car and couldn't get it to start and because I had fuel and compression, but no spark I immediately started t/s near the icm. Only because of chance I was loosening the icm harness when I decided to try and start it again that I got spark. What I found is that if I tightened the icm retaining bolt too much I would kill the engine, and I witnessed the engine begin to struggle as I slowly tightened the bolt. After leaving it in a good spot and being curious - for fun I pushed on either side of the harness and found all the same symptoms. After taking the harness off and inspecting under the rubber grommets I noticed the plastic casing was cracked around the center bolt area. Somehow (engine vibrations + heat causing expansion) the signals were getting shorted to ground via that bolt.
To make a long story short I was able to replicate the random engine struggle and even recreate a bad CKPS symptom (engine stall, tach falls to zero, tcs light) only because that signal goes right through the harness. So do yourself a favor and before replacing other parts that may or may not also need replacement; with the engine running BE CAREFUL DO AT YOUR OWN RISK THERE IS MOVING PARTS CLOSE TO THIS AREA push on either side of the icm harness and see what your engine does. If you have a good harness (that has never been over tightened) your engine should stay running and your problem is caused else where, otherwise you may need to get a new icm harness. I would suggest Morad Parts Company as the dealership will want quite a bit more money for a new one.

[gutterjrn]

When driving with the MAF unplugged I didnt get any hesitation while driving, only the idle was a little erratic which is to be expected correct? I am going to continue driving a couple more days before ordering the MAF just to be sure.

Where would be the best place to buy a new MAF, what are the thoughts on buying a new one from GM parts direct ($180). Any other suggestions? Thanks.

[gutterjrn]

Or is it worth it to buy some MAF cleaner and try to clean it first, as far as I know its never been cleaned.

[richtazz]

The MAF was a god call Tim, not sure why I didn't suggest it, must be CRS kicking in.... Gutterjrn, you can try to clean it, but regretfully in my experience cleaning rarely works.