i have a 91 Isuzu Rodeo 4x4 3.1 and im having problems with it not idlin right the rpm needle jumps up and down while idling and sometimes dies and so far ive changed

rebuilt engine
throttle body
TPS
idle control valve
injectors
battery
spark plugs and wires
distributer, cap and rotor
map sensor
new vacuum lines

any suggestions on to fix this problem?

check for vaccum leaks? got all your hoses going to the right places? MAP sensor?

installed new vacuum lines when i rebuilt the engine and i switched the map sensor out 2

its drivin me crazy

i used to have this problem with my 92 amigo. the problem with mine was the connection for my fuel pump was going bad. so i cut the connector, connected the wires and it never idled like that again

Is your 3.1 engine an Isuzu? or GM V-6? If GM V-6, you could follow the manual proceedures for minimum idle setting, and base timing adjustment. Both of these have an effect on the range of operation of the idle air control valve, as would a vacuum leak (would drive the IACV all the way shut). Also, these proceedures are best to do when replacing some of the parts you mentioned in your list (not to mention resetting the ECM and pulling codes, if any, to get the ECM's opinion on the matter). If the IACV is operating in one extreme or the other, it is likely to get stuck or wear out prematurely. If there is something wrong with the IACV (btw, new parts fail too) such as a sticky point in its range of operation, it won't be able to respond fast enough to engine speed changes and will often cause the idle to fluctuate heavily and stalls.

The minimum idle setting proceedure involves disabling the IACV. You could use this to eliminate the IACV as the cause, or at least to gain more insight to the problem. For example, per the proceedure, you could disable the IACV and instead of setting the throttle stopper screw to get the spec minimum idle, set it to get approximately the normal idle speed. If you still have the idle problem, then you can feel relatively certain that the problem isn't caused by an IACV failure. However, if the engine runs smoothly with the IACV disabled, then the problem might be with the IACV, or the ECM's ability to operate it properly. And, during the minimum idle setting, while the engine is running smoothly, it's a great time to check the base ignition timing.

Other than that...Spark plugs in good shape? Gapped correctly? Have you pulled all the plugs to see if you can isolate the rough idle to a particular cylinder? Compression test? Are the rocker arms fixed on this engine? Or adjustable? If adjustable, you may want to confirm proper valve adjustment. Consider the exhaust valve being a wee bit too tight. Might run OK cold, but as the engine warms up, you could lose compression enough to effect the idle, but not so easily noticed at speed.

Good luck !

Is your 3.1 engine an Isuzu? or GM V-6?

The 3.1 is a GM engine... the Isuzu engine is a 3.2 that showed up later on.
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