High RPM on start

[tycho]

First Post:

1989 Jeep Wagoneer Limited
4.0L, Inline 6, 155,000km
driving habits: daily with the 89 jeep, work related plus recreational

Purchased the wagoneer about 4 months ago, been busy fixing small things, suspension, brakes, cooling system. Have come accross a new problem, not all the time but 3 or 4 times a week when starting the wagoneer the rpm's instantly shoot up to 3000 and stay high for about 30 seconds then comes down to normal idle speed. This is a bit scary as I do not want to damage internal parts due to lack of early oil circulation. This does not happen every time on start ( right now anyways), and it doesn't seem to happen on the morning vehicle start. Any feedback on areas to check for faults would be appreciated.

Luke

 

[redlightstalker]

try checking worn cables and linkages.hose down the tb withsome good tb or carb cleaner then lube up all moving parts on outside of tb.check all your vac hoses too.

 

[90Xjay]

First Post:

1989 Jeep Wagoneer Limited
4.0L, Inline 6, 155,000km
driving habits: daily with the 89 jeep, work related plus recreational

Purchased the wagoneer about 4 months ago, been busy fixing small things, suspension, brakes, cooling system. Have come accross a new problem, not all the time but 3 or 4 times a week when starting the wagoneer the rpm's instantly shoot up to 3000 and stay high for about 30 seconds then comes down to normal idle speed. This is a bit scary as I do not want to damage internal parts due to lack of early oil circulation. This does not happen every time on start ( right now anyways), and it doesn't seem to happen on the morning vehicle start. Any feedback on areas to check for faults would be appreciated.

Luke

Luke
Welcome.

Give us a little more info on the engine. Is it fuel injected?
I've had my 1990 do that once in a while, when It did, I shut the key off asap.
That is not good starting and reving high like that. I seem to remember cleaning my throttle body with CRC really good and spraying all of the linkage with a WD-40 type lube spray. If it is a EFI engine, you could have a TPS(throttle position sensor) sticking or not working right. I also took mine off of the throttle body and cleaned all of the sensors with sensor safe cleaner.
There is a ring of carbon that builds up inside the throttle throat that causes the butterfly to stick, that whole thing needs to be dissoved with a good cleaner. I took a red rag soaked with cleaner and cleaned all of that ring off. Be careful not to drop anything down the intake.


90

 

[hankdz]

Had similar problem with 92 4.0 fi. Not when starting but when running. Would hesitate then surge. Low rpm to high rpm. Did clean job as recommended in other threads. Helped a little. Changed fuel filter. Solved problem. Only thing I can figure is there must have been some dirt that stuck and unstuck by itself.

 

[Utah_jeepster]

In 1989 jeep stop making the full size wagoner line but made several wagoner/Cherokee models. That came with the 4.0l
First check to make sure the Throttle body is clean from carbon/ varnish. Also check idle speed control motor is functioning correctly. Does it idle ok after it warms up. If so check for leaking intake manifold gasket while the vehicle is cold. Reason is that the manifold expands once the vehicle warms up and seals the leak.

 

[tycho]

Maybe thats an explanation for my engine clicking sound that goes away when the jeep warms up as well.

Havn't had time to check TB yet with these darn holidays.

 

[earlyd]

I have this same problem with my 1994 Grand. However I was told by a mechanic that it is the computer and thats a $900 repair. In addition he says it will open a can of worms replacing it. Something about the previously replaced parts not being recognized and throwing new codes out. I've been tolerating this for almost 2 years. I just the engine down until it starts normal. Sometimes it goes away for weeks. Scary and I love my jeep.:mrgreen:

 

[MudderChuck]

First Post:

1989 Jeep Wagoneer Limited
4.0L, Inline 6, 155,000km
driving habits: daily with the 89 jeep, work related plus recreational

Purchased the wagoneer about 4 months ago, been busy fixing small things, suspension, brakes, cooling system. Have come accross a new problem, not all the time but 3 or 4 times a week when starting the wagoneer the rpm's instantly shoot up to 3000 and stay high for about 30 seconds then comes down to normal idle speed. This is a bit scary as I do not want to damage internal parts due to lack of early oil circulation. This does not happen every time on start ( right now anyways), and it doesn't seem to happen on the morning vehicle start. Any feedback on areas to check for faults would be appreciated.

Luke

Three (main) reasons for this happening with the Renix (87-90) XJ's. The idle air controller gets sticky, you can clean it (and the seat in the throttle body), spray behind the IAC piston with some spray oil without moving the piston (don't mess with the piston) and then let a little synthetic oil run behind the piston ( I use regular old synthetic motor oil). The IAC needs a strong battery to work well, one sign of a failing battery can be sporadic IAC function.
Be careful with the IAC and TPS bolts/screws, they have a tendency to snap off if forced too much. Stick your torx socket in the end of the screws and tap a few times with a hammer to help break up the oxides that weld the screws to the TB. Keep spray oil, solvent or water away from the TPS (they leak).
When the TPS (throttle position sensor) starts going bad, has questionable grounds or connections, or gets wet with water or oil, they can do this. High idle at startup is a common problem after a motor wash.
The typical Renix hot start, when shutting the motor down and restarting it hot, it's typical to get a high idle. The problem can be reduced but I've rarely seen anybody completely eliminate it. One reason the older Jeeps (Renix XJ's) were recalled was to put in an interlock, so the shifter couldn't be shifted without pushing on the brakes, I don't think Jeep ever found a complete solution either.
A clean IAC, a good TPS (grounds, wiring and connectors) and a strong battery can help minimize this.
Mine rarely does this anymore, it's gotten to be very occasional and not nearly as radical as it used to be. Throwing parts at the problem may be a waste of money and effort. My solution was good grounds, low ohm resistance readings on the TPS wiring, a strong battery, cleaning a lubricating my IAC twice a year.
Weak throttle plate springs or sticky linkage can also cause this, as can vacuum leaks. But more often cause a constant high idle, rather than the surge.

Welcome to the world of Renix, like a high maintenance spouse they often require constant attention.

 

[Bounty__Hunter]

'05 post.

 

[Jeeper99]

'05 post.

:lol::lol: Dang, somebody's been reading back through the forum! p0p

 

[Bounty__Hunter]

It gets me on occasion too when a thread is brought back from the grave.