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Erratic Idle

tireroastin93XJ

NAXJA Forum User
Location
Sedalia,Mo
The idle on my 93 likes to surge between ilde and about 1700 rpm. It doesn't do it all the time, and it does it both cold and warm. Sometimes it will start up normal and then jump up and stay there or it will immediately idle high. Shutting it off and restarting doesn't help either. It will just stop doing it on its own. I've checked for cracked vacuum lines and replaced a few. Any ideas?
Mike Harris
 
tireroastin93XJ said:
The idle on my 93 likes to surge between ilde and about 1700 rpm. It doesn't do it all the time, and it does it both cold and warm. Sometimes it will start up normal and then jump up and stay there or it will immediately idle high. Shutting it off and restarting doesn't help either. It will just stop doing it on its own. I've checked for cracked vacuum lines and replaced a few. Any ideas?
Mike Harris
I just had fixed my 93', I had a high idle problem with mine. I put the wrong intake/exhaust gasket on and had a major vacuum leak. The MAP senor is the one that reads the vacuum preasure and sends it to the CPU. So either you still have a leak or your MAP may be out.

A quick vacuum check is, while the motor is running. Place your hand on the top of the Throttle body. If your engine stops, then you have no vacuum leak. If it just sputters but keeps running. Then you have a vacuum leak to find.

HTH
 
When the TPS goes out, it normally produces a high idle. If you have an automatic transmission, then you may also notice some weirdness to the shifting, since the TPS sends a signal to the Transmission Control Unit as well as the engine computer. If you search "TPS" you will find lots of info- the basic test is to connect a voltmeter across two of the terminals on the square connector and look for a smooth progression of voltage change as you rotate the throttle (key in run position, engine off). Wires are lettered A-D on the connector- from my notes:"In adjusting my TPS I got only 4.6V as you did at the AD pins. I adjusted to 82% at the AB pins and it runs great and shifts fine. I don't think that 4.6V at AD requires any ground modifications." The three wires are ground, power in (between 4.5 and 5.0 volts) and signal out (voltage varies with throttle position).
A vacuum leak is more likely to be semi-constant; the intermittent nature of your high idle suggests sensors....but a vacuum leak is the other likely candidiate, check it too. If you do a search for vacuum you should find hints on where the likely leaks are (line under the battery, cracked vacuum reservoir blimp in the front bumper, etc.). 4xBob
 
Forgot to add: TPS is only adjustable on the 1990 and earlier (Renix electronics) XJs. You only need to look for the smmoth progression of output as you change the throttle position- nothing to adjust on your 1993 XJ. 4xBob
 
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