hi i have a 1990 jeep xj when u start it go up to 800 rpm but then will die down to 100 then go back up to 800 and go back and forth but when u give it gas it run fine but when u let off the gas it will stall i put a new idle air control valve but it did not make a difference so any other ideas would help thanks

 

1. Be sure that your exhaust gas recirculation is working properly. More on that below.

2. Review tuneup hardware status. Fresh Champion plugs gapped to .035, new plug wires, distributor cap and rotor

3. Did you thoroughly clean the throttle body yet? If not, you should. They get carboned up over time and miles.

4. Test AND adjust your throttle position sensor. Yours is adjustable.
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Originally Posted by Factory Service Manual
TESTING
EGR VALVE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.

 

hi thanks i will check the egr valve tomorrow and and clean the throttle body and the position sensor thanks again for the help i will let u know if that help

 

i say check EGR system and check go over vacuum lines that go into the intake. if a vacuum line is broken or disconnected from intake it could be the cause of the issue.