Hey guys, it's been awhile. Unfortunately, I'm back because I'm having some problems with by car. 02 GTP, little less than 120k on the clock. I'll list all of the problems, although I don't know for sure that all of them are related.

For the past few months, I've been getting poor MPG. It went from ~19 with normal driving (not flooring it but not granny-ing it either) down to ~15 mpg with granny-ing it. Money has been tight, so I hadn't been able to try working on it until lately. I changed the spark plugs about 3-4 weeks ago, but after using about a full tank I hadn't seen any improvement.

Then, a couple days ago, I was leaving work and it started idling high. In Park/Neutral, it idled a little above 2k RPMs, and in drive it was about 1600 RPMs. It was noticeably more difficult to stop than normal because of the higher RPMs. Once I got on the road, I noticed it didn't want to shift up. I had to let fully off the gas before it would shift, and when it did, it would sometimes surge forwards a little, just a single surge. It would shift down just fine.

I let it sit until I had a day off and either used my girlfriend's car or my mom's car in the mean time. I went to drive it today, and not only is it still idling high and not shifting up unless I let fully off the gas, now, when I slow and it wants to downshift, it surges forward several times while I'm decelerating. I simply drove around the block in my neighborhood, and when I parked it at home, it was idling at about 1900 RPMs in gear and it jumped up to 3000 RPMs when I put it in both neutral and park.

What's really odd is there is no SES light. I was going to drive to Autozone today and have them scan it to see if maybe it was throwing a code and the bulb was burned out or something (I figured it was worth a shot), but with it acting even worse than it had been, I just went around the block.

I also cleaned the K&N filter I have a couple months back to try and help the MPG, so I know the filter is good.

Any suggestions? The car not wanting to shift up and surging on downshift is what's worrying me more than anything else...

I literally just got back in from fixing a similar issue with wierd idling issues that sound almost identical to yours. At first i was leaning towards the IAC. And someone from the forum advised me to test them. Upon testing they turned out fine. It gradually got worse. Then it started acting up on starting. After driving it and then going in somewhere and coming back to start the car it would take several cranks to start. Problem for me was the fuel pressure regulator. Good way to check is to pull the vacuum line from the regulator and see if its wet with gas. For me it was and upon replacing it all of 30 mins of time with a towel two flathead screwdrivers. I drove several times back and forth to town. Car is not idling funny not shifting crazy. And seems to have fixed the issue. I would check that.

If the SES light comes on when you turn the key the bulb is good.

Unplug the TPS and see if the motor's rpms do anything. If it does then it's the TPS.

No changes then with it plugged in un plug the maf. Listen for changes.

If it drops it's the MAF. When you cleaned your filter did you over oil it? If so it could dirty the MAF and cause problems.

If still no changes start searching for a vacuum leak.

Best guess is you probably have a vacuum leak or a bad sensor, but I'd get the check engine light fixed so you can get some codes, if it has any. I've seen GM cars do strange things when the check engine light burns out, or is removed for any reason.

@pontiaclivson, do you have a pic that shows where the fuel pressure regular is, so I can check it? (Or Blackarrow? I'm sure you do. lol)

And Herc, I just checked and the SES light does work. I hate it when I overlook the simple things like that...

A dirty MAF is one of the things that I was thinking, especially now that the idle is crazy, but would that or the TPS affect how the car shifts? I will check them regardless, but I was just wondering if they would affect the shifting or if that might be a different issue.

Here's a pic of the fuel pressure regulator, with vacuum line attached:



From this write up: http://grandprixforums.net/injector_oring.php

I don't know but it's worth getting the idle issue fixed and go from there.

http://www.grandprix.net/forum/ubbthreads.php?ubb=showflat&Number=213500&#Post213500 theres the post i posted about the issue. and i described alot of the issues im not super mechanic. so i dont have explanations of why it does those things but if i had to guess the extra gas going through the vacuum line into the throttlebody makes it rev higher to try and offset the extra gas. it shifts hard because the engine is reved higher and not going any lower. and it would also explain your bad gas mileage. just sharing from experience. part was 52.99 at advanced. and immediately after changing it the engine sounded different and didnt feel as rough as it had. i hope it helps i was gonna get pics but was beat to the punch and glad i was too. cause would be ashamed to put pics of my dirty engine bay up.

LOL, yeah...no worries on what you got. Guarantee that I got you beat.

At least yours isnt missing pieces!


Notice shiny new fuel pressure regulator

Please let us know what the issue turned out to be when you figure it out.

Well, here's the latest. I went to move the car into my garage and had trouble starting it. It turned over, but took several tries to catch. That could just be because it sat there for almost a week, and after starting it a couple times it seemed to start fine, so I'm not too worried about that.

I unplugged both the TPS and the MAF sensor and the RPMs didn't change.

I pulled the vacuum line off the fuel pressure regulator, and there didn't seem to be any fuel. However, since I haven't driven the car for several days, could that be why? Should I go drive it? Or was it running for 5 minutes long enough to tell me whether or not that was the problem?

While it is in idle, the RPMs would be at about 2200. They would try to drop, but as soon as they got down to about 1500, they would come back up. Seemed like it was trying to keep itself from stalling. It only seemed to do that after I put it in drive and back to neutral or park - if I don't ever put it into drive, it idles high but stays steady.

This will probably sound like a stupid question, but if there is a vacuum leak, can you hear it? I've never had to deal with one so I'm not sure. While the car is idling, it sounds like I may be hearing a sucking noise. It's hard to tell, though, because with the engine idling so high, it's making a lot of noise in a small space like the garage (well, the front half is inside, the back half is outside so I don't die lol) and with the loud *** K&N intake, there's a lot to listen over. Of course, the noise I'm hearing could also be coming from the intake itself.

I've never been able to hear vacuum leaks, and that was with my bone-stock GT. Best advice is the most repetitive, unfortunately: chase the lines. Something else I've noticed is that these vehicles are starting to see the IAC fail quite a bit. I guess those sensors are reaching the end of their life. Good news? OReilly has Borg-Warner sensors for $37. That's not to be implied that your IAC is bad, because I'm not sure that's the case. With the Camaro, my car was WANTING to stall, which is not your symptom at all.

How do I check to see if the IAC needs replacing?

Hit it and see what happens. If the idles comes down you've found your problem. They may not always come unstuck with a tap but it works often enough to suggest it.

Another way to see whats going on is using a scanner and view the live data. See what the commanded idle is vs actual. Then it's really helpful if you can run a test on the IAC and adjust the idle from the scanner. I don't know if you or a friend has one with that feature set, but if so it's very helpful.

OK, apparently I got my sensors mixed up. That's what happens when you only know a little about cars to begin with, and then don't go under the hood for anything more than an oil change for a few months.

Anyway, new results:

Pulled the MAF sensor. Doesn't look to be very dirty, but at Blackarrow's suggestion, I will spray CRC Maf Sensor Cleaner anyway.

Tapped the IAC sensor, and nothing happened (sadly, I don't have or know anyone with a scanner).

Unplugged the TPS. RPMs dropped about 200-300 RPMs, and when I pulled it back in, they slowly climbed almost 1000 RPMs, which put them even higher than before I removed it.

Another thing that was interesting was when I put my car in reverse to partially back it out of the garage, the RPMs were very quickly fluctuating about 800 or so RPMs. Again, it kind of seemed like it wanted to stall. As soon as I put it in neutral, it stopped doing that and didn't do it again, either in Park, Neutral, Reverse, or Drive.

Herc, I know you mentioned if the RPMs drop when I unplug the TPS, the TPS is bad. Does what it did sound like it needs to be replaced?

*EDIT* And, if I do replace the TPS, which one of these from Advanced Auto Part should I pick up?

Bump for suggestions?

I'm not a fan of throwing parts at issues but in this case if I was in your shoes and I unplugged the TPS and the rpms dropped 200-300 then I'd buy a new TPS and go from there.

I had an 89 Ford F-150 with a manual that had a bad TPS. The truck wanted to idle at 2000 rpms. Talk about fun limping it home trying to feather the clutch. Replaced the TPS and the rpms dropped back to a normal 900 at idle.

Well, I replaced the TPS and sprayed the CRC cleaner on the MAF, and now my car won't even start. It'll crank just fine, but it won't catch and fire up.

Like I said before, I had been having trouble getting it to start but I just figured it was because it's doing a lot of sitting.

Installing the TPS is as simple as taking the old one off and putting the new one on, right? Nothing I missed there?

I'll take the new TPS off tomorrow after work and put the old one back on and see if it'll start then. In the mean time, do you guys have any other suggestions?

*EDIT* What makes this even more frustrating is when I put my car in the garage, while it was hard to start, the RPMs were more or less fine. Drove it around the block, and while it still shifted hard, the RPMs were only slightly high. WTF?

Sorry about no replies my cpu bit the dust had to wait on newegg to ship another. In my problems with it gas wasnt present when just idling and if you havent had it out of the driveway for a while the gas would have evaporated. it doesnt take long especially around the heat from the engine. take a couple of laps around the block and then check it again. make sure you are hitting the gas pedal though and not just rolling around.

Ok, update: I took that TPS back and got another new one. Car starts now, but it still takes it a couple seconds, and I usually have to have the gas pedal at WOT for it to catch.

It also didn't fix anything. Sometimes it idles fine (why I don't know) but it usually idles real high, and it never shifts unless I let off the throttle.

However, when I changed the TPS it did finally give me an SES light, code P0123. That code? Means there is a problem with the TPS. Grrr. Googling it also told me that it could be a short in the wiring. I'm at work now, but I will follow the wiring and see if I can find any problems.

In the mean time, does anyone have any other suggestions?

And one more question....is driving it going to cause any further problems? I'm not driving it much, but to work and back, which is 10-15 minutes each way yesterday and today.

Ace, you do realize that when you reinstall the TPS you need to have that little coil spring wound like about 1/8 of a turn. Kinda weird... my buddy said he didnt do it how you're suppose to and had really weird shifting/throttle response.

I'm pretty sure I did it right. When I put it on, I twisted it about 90* clockwise first, then put it on and rotated it back counterclockwise so the thing in the throttle body would catch the spring in the TPS. does that sound right?

I know something was up with my old TPS because on the new one (both of them), if I twist it further counter clockwise it will spring forwards if I release it. My old TPS would stay in place, so the spring was obviously broken or something.