Throttle Issue

[nvygun]

So I am finally wrapping up replacing the head gasket on my 99 XJ and I got everything buttoned up and fluids topped off and I turned the key and it fired right up. Which would just be awesome but it the engine ran like the gas pedal pushed to the floor. I checked the cables and tried again and the same thing. Going to double check everything tomorrow but I am kinda at a lose as to where to start or what may cause that problem. Anyone ever have this issue or have any trouble shooting ideas I could use?

[4.3LXJ]

Troy, sounds like you have a hefty vacuum leak. Check your intake to start and all hoses, especially the brake booster hose

[Brasscatz]

I'm going with vacuum leak too. Interested to hear what the culprit was.

[olds-cool]

Is the butterfly closed all the way? If so, I'd have to agree that there is a vac leak somewhere that is allowing extra air to mix in. Mayb you missed a hose or one of those plugged off connections lost its cap in the process of moving stuff around.

[nvygun]

As it turns out 4.3 is exactly right. So this is what I did today to check it all. I cleared the memory and checked the OBD II and got back to codes. The first was PO123 (TPS to high) and the second PO505 (Idle Control System malfunction) so ran to NAPA and picked up a new TPS. Because when I had the head off I did a through cleaning of everything including throttle body and thought that I damaged it but it didn't fix the problem. Double and triple checked everything again. Everything is connected properly so I removed one vacuum hose at a time and plugged the manifold and still nothing. So as my frustration grows I am back on the forums looking for a smilier problem and still nothing then decided to crawl under the jeep and recheck my work and there it was! The intake manifold didn't catch the rear alignment pin. Which you can never tell from looking from the top but underneath I can see at least an eighth inch gap so at least the last two cylinders where sucking in a ton of air. I'm just surprised it started so easy with that much of a gap. Thanks all for the help and advice and I am now a smarter XJer! Woot! Oh yea, won't get fixed till next week since it to close to game time.

[nvygun]

Now that I have the intake on the right way my $900 XJ is running great! Took it for a quick test drive and great acceleration and everything was sounding great until... I made a right turn and then this awful sounding grinding noise. Also under heavy breaking too. It's the brand new pace setter headers I just installed being grinned by the u-joint of the front axel. Now I no why the stock header was all smashed in that same area. Wondering if this can be caused by worn out motor mounts?

[4.3LXJ]

Yeah, better check those motor mounts

[ALS XJ]

Hey Steve...I've got a wacky idle problem on my '92...maybe you can give me your input. Starts right up, then about 1-2 min into idle, it revs to 1200-1500rpm, then downto pre-stall about 500rpms. Removed the TB, cleaned it well (new TB gasket), tried cleaning, then replacing the IAC...better for a day, then the problem came right back. Does the same on the road as well...then goes away and runs fine! Drivin' me crazy...any input from you would be helpful...thanks!

[ALS XJ]

Woops, I forgot to mention, the idle goes up and down over and over again...BTW what does the brake booster have to do with this issue...still trying to figure out this XJ thing!

[4.3LXJ]

Thought I posted on this, but maybe someone needs to learn me how to post :D

Anyway two things come to mind. First take the battery cables off and touch them together and reinstall. The computer will have to relearn and that may be what is needed. The other thing is to check the timing. If it is off it can cause that surge as the computer tries to juggle bad timing and idle speed

[nvygun]

So a set of brown dog motor mounts on there way. Hope that's it. Seems XJ motor months are a pretty big issue.

[ALS XJ]

Thanks Steve...I did disconnect the negative before I reinstalled the IAC...but I did not know about touching the neg-positive cables! I hope this does it...as always, YOU know your XJ's! Thanks again....you da man! By the way, I've heard you had a hand in building the Ark:D

[4.3LXJ]

Thanks Steve...I did disconnect the negative before I reinstalled the IAC...but I did not know about touching the neg-positive cables! I hope this does it...as always, YOU know your XJ's! Thanks again....you da man! By the way, I've heard you had a hand in building the Ark:D

Yup, seems to have worked well too:sign0181:

When you disconnect the battery cables, you have to disconnect both to reset the computer. One side connected is enough to keep everything the same

[ALS XJ]

Gotta work today, but I'll try this afternoon...I'll let ya know if it worked!:pray: Thanks again, Steve!

[ALS XJ]

Ok...I tried the battery disconnect procedure...problem still there, so I found another thread on Jeep Forum. Disconnect the positive cable from battery, ground to the A/C compressor for 30 seconds, re-connect to battery, turn ignition to "on" position (do not start the jeep), turn headlights on, turn headlights off, turn off ignition...then start the jeep. This procedure seems to have worked, took the XJ for a ride...no issues. Time will tell,:pray: I'll keep you all posted. Thanks for all your input and help Steve!:D

[ALS XJ]

OK...issue remains, even after replacing the TPS, and resetting the computer. Maybe it needs more time to "learn"????? Does have 268k on it...maybe a new computer? Driving me nuts! Oh well, almost time for that shiny new "Stroker" I've been eyeballin!

[nickyg]

Just my $.02, I'm no expert.. The only 3 times I had an idle problem was due to a bad TPS (easy check with a multi tester) A vacum leak in the canaster in the front bumper (A rock or something put a huge hole in it). and a plastic bag got sucked into the airbox. (that was a hard one to figure out). From the way you described I would guess TPS, then vacum leak. By the way the brake booster has a huge vacum line in it.