bonesxj
NAXJA Forum User
- Location
- running springs,ca
After starting my 89 XJ, some times the RPM's go up to 2000 and stay. I have to turn it off and on a few times before the RPM's go back to normal at idle. Any thoughts...
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High RPM's
- Thread starter bonesxj
- Start date
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
sounds like a faulty Idle Air Control Valve. (IAC)
Flyfisher
NAXJA Forum User
- Location
- Billings, Montana
I would agree with the IAC. My '89 does that too...especially with cold starts when it's cold outside (less than 20 degrees). After it finally idles normal, it won't do it again until the next cold day/cold start.
Cleaning the IAC helps for a while, but so far hasn't seemed to be a permanent fix...might have to spring for a new one!
Also, be sure to check for vacuum leaks...sometimes cold rubber doesn't seal so good and a leak will cause the high idle.
Cleaning the IAC helps for a while, but so far hasn't seemed to be a permanent fix...might have to spring for a new one!
Also, be sure to check for vacuum leaks...sometimes cold rubber doesn't seal so good and a leak will cause the high idle.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
I have a three-page "High Idle" document--I don't remember where it came from, I didn't write it, so I won't post it and take a chance on copyright issues--however, I will gladly forward it to anyone that PMs me their email address with "High Idle" in the subject line.
- Location
- MilkyWay Galaxy
Change the MAT sensor first, or just clean it first and test it.
Also See:
http://www.naxja.org/forum/showthread.php?t=905849&highlight=renx+files
http://www.naxja.org/forum/showthread.php?t=1072534&highlight=cruiser54
- Location
- MilkyWay Galaxy
One can test the IAC to see if it is causing the high idle by disconnecting it at a normal idle. The start it cold, run it, shut it off start it hot, and see if the idle changes. IF the idle changes suddenly and significantly during the tests it is probably a vacuum leak or fuel issue, like injectors and O2 sensor battling it out.
The IAC changes the idle but only when the ECU tells it to do so. A vacuum leak will make it idle high all the time (unless the leak rate somehow changes, hot to cold..)
The IAC changes the idle but only when the ECU tells it to do so. A vacuum leak will make it idle high all the time (unless the leak rate somehow changes, hot to cold..)
- Location
- Roanoke VA
Our 89 MJ does this as well. I have a new IAC and shut down relay(sets the IAC for the next start). I have a new MAT and CTS. There are no vac leaks.
It still does this. I'm starting to think its a trait of the 89 ECU.
It still does this. I'm starting to think its a trait of the 89 ECU.
- Location
- MilkyWay Galaxy
Have you followed Cruiser54's Renix sensor ground fix procedure?
One of the things I finally did was to catch it at high idle and go testing the running system at high idle with a volt meter, testing each sensor ground for excess back voltage (sign of a local ground issue), and for odd sensor readings that were too high or low!!! I found multiple sensor grounds that were bad inside the harness itself!!!! Crusier54 has documented this too!
Does yours do it all the time, high idle, or randomly, or hot or cold?
In some cases we find it necessary to undo "Uncle Bobs" prior work to fix steady, constant (vacuum leak sorta) high idles.
- Location
- Roanoke VA
Mike, my 89 only revs high on start up then levels off to a smooth normal idle. It acts as if its setting the IAC too lean but it starts great and much faster(less turns) than my 90. It starts quick like a HO but just has the high rev.
- Location
- MilkyWay Galaxy
Check the fuel pressure regulator's vacuum line for any gasoline, maybe an early small leak. Also could be an injector with a slow small leak. Only way I know to check that is a fuel pressure gauge, leak down test, after turning off the jeep, to see if pressure holds or drops.
We get so use to the usual suspects (ground isues and vacuum leaks) we sometimes forget the unusual ones. Yours could be excess gas sitting around at start up.
- Location
- Roanoke VA
Great advice! i will look into that. The injectors are replacements but it still has the original FPR in it.
