1990 renix rpms drop

1990 renix engine ,rpms are at 1000, when you put it in drive they drop to 500 and it acts lik it is going to stall if you turn a/c on it stalas out

A**uming the transmission is a AW4 automatic.

The correct idle speed is 700~750 RPM in DRIVE. It is checked after the engine and transmission are both up to full operating temperature--after about 20 minutes of operation. Second set of hands, parking brake set AND with foot on service brake pedal, shift transmission into DRIVE and check the idle speed.

Your problem is most likely the IAC/IAC port in the throttle body. Buy yourself some throttle body safe aerosol cleaner. Remove the IAC, clean the throttle body inside, the IAC port, the throttle plate. Clean the IAC but be careful with it--you can break the pintle and then you are going to need a new one. Use the spray cleaner, cotton swabs, old toothbrush (or your roommates toothbrush). Put it all back together, get it back to operating temperature and check the RPMs again.

The IAC is a stepper motor that receives an extend or retract signal from the ECU to control the idle speed--there is no mechanical adjustment for the idle. There does exist a small allen screw that can move the throttle plate--don't screw with it, it is NOT for idle adjustment, it is there to prevent the steel throttle plate from slamming fully closed in the alloy throttle body and damaging it.

The IAC can become "lazy" with age and then it should be replaced.

PS--don't provide power to the IAC when it isn't mounted, it has no built in stops and overextending it will break it.

Good luck.

x2 on what joe said

if that doesnt fix the problem, check the condition of the a/c clutch pulley and test the a/c clutch relay in the relay center.

x3. Had the same issue on my 90 Renix

Welcome to the club...another '90 here with similar issues except mine does it regardless of the AC being on. Plus mine has a miss at idle...sometimes.

mine does high and low idle...and at low idle will die about 50% of the time. Always starts back up...except yesterday when it melted the CPS wires. But even with a new IAC and rewiring the CPS (plan to replace soon) it still does it.

We're going to hook up a scanner and actually drive around to see what is causing mine to do this.

Good luck. Out of 8 XJ's and 2 MJ's this is my 1st renix jeep. I like it so far but man are they crabby.

Replacing the IAC on my Renix only fixed the high RPM issues. My low idle issues went away after I replace the Throttle Position Sensor.

great site for testing and diagnosing the renix fuel injection is www.lunghd.com and go to on site tech. great how to's and a link to the renix injection system.

get yourself a multimeter and the reference charts/tables for resistence and voltage values for the electronics.

only scanner i know of that can read "live" data is a snap on 3500 with the renix adapter.

there are also some threads that must be at least 5-6 pages long if you search for renix and high idle.

here is one that covers most everything about idle issues.

http://www.naxja.org/forum/showthread.php?t=905849&highlight=renix+idle

89xj said:

only scanner i know of that can read "live" data is a snap on 3500 with the renix adapter.

Click to expand...

That's the one we're using (my friend owns one).