weird rpm's at start up, explain?

not sure If this is oem or not but this has happened twice now so Im asking about It....

I went and started the XJ this morning and It was Idiling at 2k rpms....It continued to do so until I put It in Drive, then put It back in park and It was fine, this morning I was on flat ground so Im not sure why It did this....

the first time It ever did this I parked overnight in a flexed position so my engine was somewhat at an angle, got In the next morning and It did as I described above, I figured It was the angle I parked at since It never did this before....

so now that Its the 2nd time Im wondering why It did this?

My XJ did a similar thing recently. I stalled it on a slight incline, restarted it immediately, and the RPMs climbed to about 2250 and then dropped back to normal idle speed. Mine's not an auto, but I wonder if our problems our related.

same prob. here with mine....I think our problems are iac related....

it happens to me every once in a while on my 98 auto xj

so 4 guys with the same problem, but still no reasoning, come on wheres the XJ guru's?

If you stall the engine and then start it right after it could temporary rise in rpm. This because it has som gas that were injected in the manifold as and after it stalled. This gas is sucked in at cause a high idle. My 89 4.0 auto has the temporary high idle. THere is a factory service bulletin on this subject. It has to do with the bonding inside the tps. It gives the tcu an faulty signal.

Torfinn

torfinn said:

THere is a factory service bulletin on this subject. It has to do with the bonding inside the tps. It gives the tcu an faulty signal.

Click to expand...

I thought this was the Renix only, I know my 90 does it every once and a while. IIRC The recall stops at 91 with the HO engine.

mines a 99 auto, the most recent time It was at 2,000 for about 30 seconds until I put the car in drive and then back in to park, then It went to a normal Idle

Mine does the same. Does this mean I should be able to take it to the dealer and have them fix it? Does anybody no the service bulletin number? Thanks.

Matt

It might be the throttle position sensor getting a little dirty. Try cleaning it off, or replacing it completely. I had a friend with the same problem, and that was the only solution he found.

http://www.autobytel.com/content/own/service/index.cfm/action/RecallsView/seriesid/11053

Torfinn

I have a '91 man HO and have never had that problem but I would tend to agree with the gentleman that suggested replacing the IAC motor. Even the TPS as the bulletin suggests and you will only be out maybe 30 minutes of easy time and about $80 or less on parts w/shipping. And I'm fairly sure one of these should solve the high rev. There shouldn't be many other issues or recalls as your XJ is fairly new....compared to mine haha. But I swapped mine out even though I didn't have this problem but for the cost of the piece of mind....The tps sensor is mounted on the rear of the tb looking from the front and I've seen them for under $40. The IAC I went local like an idiot and paid $52, but I needed it now. They are about $38 or so on here and this is located on the left side of the tb looking from the front. you will also find the map sensor on the right, looking from the front, but this shouldn't be the cause of the problem I wouldn't think. This WAS my issue due to a change in perf. options I added and it threw my fuel curve outta wack so I am putting in a map modifier that is adjustable and is about $80 plus shipping. It allows you to adjust the voltage as needed to lean out the mixture...or so I'm told haha. Hope any of this crap helps and GOOD LUCK!

Mine starts at 2.000RPM's at times to. To check what is causing I disconnected a sensor that's in the front of the TB, when I disconnect it the rev's went up, and after I connect it it went back to normal. I changed the TPS because I had some issues with the Kick Down, so I'm pretty sure the TPS is not the problem.
I don't know the name of the sensor that is in the front of the TB, so if someone knows it, please say it. jeje.
Thanks

Ahh. my Jeep is a 1990 Auto.

my 93 H.O> revs up to 2000rpm at start then drops to 900 rpmk after a couple of seconds and stays there .i was thinking the high rev was kicking off the choke at high rev prematurely.

Mine stays at 2000+ for a few minutes. Actually somtimes it starts to rev more maybe to 2300.... I'm pretty sure it's not the choke.

There was a recall on Jeep TPS (throttle position sensors) causeing high idles at start up. Mine has done it a few times, and I took it into the dealer, and now it starts just fine, no high idle. Check into that.

Mines an '88 and used to do that every morning on start up, I changed the engine (for different reasons) and it hasnt done it since, but the motor i replaced it with came out of an '87....

The symptoms on my 88 XJ 4.0 weren't exactly like those described, but they were persistent, and very satisfying to finally isolate and repair. It may give folks ideas to work on.

My XJ would idle fast (c. 1100 - 1500 rpm) at times, especially in Park, and moments later drop to normal (c. 800 or so). Especially likely after a stop and restart. Finally turned out to be a bad vacuum solenoid on the drivers side inner fender. Idles like a champ now, and had the best emissions test result in years a couple of weeks ago.

heyyy mine did it too during the hotter days...and then stopped when the cold weather started...( I dont know if thats related but anyways) it hasnt done it since but now warm weathers startin back up so we will see...I also tested my TPS and it was ok. Ive got an auto.

my 89 does the same thing too it idles around 22-2300 on startup hot or cold doesnt seem to affect it an then once u run it hard for awhile it idles around 2200 but it lopes between there an 1450 kinda i dunno whats the word erraticaly basically its all over the tach