moon rev when starting

[one_bad_MJ]

my MJ likes to rev to the moon sometimes when i start it anyone have this problem?? 4.0L

 

 

and how doy ou like up your "track" with a adj trackbar. I'm not retarded i have it on. i just need to get it centered whats the trick?

 

i got my jeep aligned since i hit a pipe hidden in the weeds and bent my tie rod under my pumpkin the other night. and my trackbar was shot so i got a rough country adj one cheap.

 

the reason i ask is because my left tire rubbs on my LCA it never did that before with the old track bar

[64 Cheyenne]

The trackbar centers the axle. If the tire rubs on the left CA, sounds like the axle needs to be moved over to the left some. Disconnect the bar at the adjustment end and shorten it till the axle is centered.

On my 88 the engine revs like that on occasion. Sometimes I shut it down, wait a few seconds and restart. Sometimes the high revs stop this way, other times I have to do it a few times. Things Ive done to try and fix it. Cleaned and adjusted the TPS and IAC motor.

Replaced the IAC motor, still does it on occasion. Seems to do it more often if I'm wheelin and I'm making the engine work hard. My next direction is to possibly replace the throttle body with one out of my XJ donor. Another possible culprit I've read about is a vacuum leak either through the brake booster (mine is OK) or the intake might have a leak, found with a tach and a spray bottle of water. Sometime this summer I'm gonna retorque or replace the intake gasket. I also read that my O sensor could be the cause of the problem, I haven't tried this yet. Tell the truth I've been "living with it", hopefully someday I'll get it sorted out.

[ComancheKid45]

Check all your exhaust bolts....even 1-2 being a tad bit loose will cause this. I went through everything (IAC, TB, TPS, ect..) and nothing solved it for more than a handfull of startups till i tightened a few exhaust bolts. Noqw I still get it occasionally but its not near as extreme or reoccuring :typing:

[64 Cheyenne]

Check all your exhaust bolts....even 1-2 being a tad bit loose will cause this. I went through everything (IAC, TB, TPS, ect..) and nothing solved it for more than a handfull of startups till i tightened a few exhaust bolts. Noqw I still get it occasionally but its not near as extreme or reoccuring :typing:

 

Kind of the direction I plan on taking, but probably be replacing the intake/exhaust gasket while I'm at it.

[jpdocdave]

i wish there was a solid answer, my first renix did this, now my mj does it once or twice month. mine seems to do it more in the cold. i wish someone could say "ya, mine did that, and i did this, and it went away" i haven't heard it yet. i'm going to replace my iac next, its mechanical and opens when starting then is supposed to close, i'm hoping the iac is sticking in the cold

 

it makes no sense that turning it off and restarting will make it stop. no gasket should act like that, you'd think. iac makes the most sense, since it moves every time its started, therefore, stopping and starting makes sense. but guys say they replaced iac to no avail.

[kyleag89]

My truck revved high when the TPS went bad.

[64 Cheyenne]

My truck revved high when the TPS went bad.

 

I wish I could say TPS, but I did adjust it with a multimeter, still same problem.

Another thing I was going to try was to swap the TB with another known good one.

Kind of funny how starting/stopping would make it Idle right. Or the fact that the only way I can replicate the problem is to "dog it" (the truck).

:dunno:

[Timmaay]

Sometimes when I started my truck it would rev way up to 2500 rpm and stay there. I would shut it off and restart, sometimes it went away other times not. But, by unplugging and reconnecting the TPS, it fixed the problem everytime. I have a different TPS in there now and I have not had the problem since.

[64 Cheyenne]

I'll give that a try. haven't done it before, because it wasn't on the A- list. Kind of didn't want to do the jump out thing, when my e-brake don't work. Why fix it, it went to the turd, 8.8 cued up, getting ready for install with 4.10s. But when were back up and running, I'll give it a try.

[bigalpha]

Check the adjustment of your throttle plate. I battled stupid high idle in mine for a long time until I found the plate was mis-adjusted. Mine still idles slightly high and weirdly but it's not at 25,000RPM anymore.

[64 Cheyenne]

Check the adjustment of your throttle plate. I battled stupid high idle in mine for a long time until I found the plate was mis-adjusted. Mine still idles slightly high and weirdly but it's not at 25,000RPM anymore.

 

Are you talking about the allen screw on the linkage side of the TB? what is the proper procedure for that?

I have messed with it a little bit, backed the screw out, didn't seem to change anything.

:dunno:

[james750]

For diag. purposes, try this: unplug your IAC before starting your truck. Fire it up and see if the idle ever comes down. If the idle stays high, plug in the IAC and see if it comes down. If it does. then the IAC is working. For some reason on my truck, the IAC sucks all the way in every time I shut the truck off. This causes the RPM to spike at first at start up until the IAC motor can move out and bring the idle back down. I don't know if all renix 4.0s do this, but if they do, thats what causes the spike in RPMS at initial startup. I know thats what causes my RPM increase.

[jpdocdave]

ya but the problem is the rpm's staying up there, and the cases i'm talking about are completely intermittent. happens once a week, or once a month. and when it happens, shut it off, restart and its fine. sometimes it takes a couple restarts, but then thats it, back to normal.

[bigalpha]

ya but the problem is the rpm's staying up there, and the cases i'm talking about are completely intermittent. happens once a week, or once a month. and when it happens, shut it off, restart and its fine. sometimes it takes a couple restarts, but then thats it, back to normal.

 

Mine did the same thing, and I solved a lot of my crazy idling by adjusting the throttle plate. It still doesn't idle correctly but it's a big help.