Wrangler Engine Revs at Startup

Whenever I start my 1993 Wrangler ( 6 cylinder ) the engine has excessive RPM ( 2000 RMP ). The RPM 'normailizes' soon after I begin moving. Any ideas what could cause such startup high RPM?

..no one has any ideas? Can't be - this is Automotive Forums!

Update....removed the idle air control valve and cleaned it thoroughly. No change - still high revs ( 1500-2000 ) upon start. However, as I view the RPM gauge, the RPMs begin to slowly decrease so that after about 5 minutes, its normal RPM at idle ( 750-1000 ).

Perhaps this has something to do with the air temp sensor? Oxygen sensor? As I research the Internet, it seems the oxygen sensor is bypassed upon startup, so I don't think the oxygen sensor is the problem.

Also, I've seen suggestions that the idle air control valve, when not installed but electrically connected, should move in and out when the ignition is turned on. Not necessarily true as I determined with both the old valve and a new valve...so something else must be inhibiting the idle air control valve from functioning correctly ( getting some sort of signal from the PCM to function ).

What say you, auto experts?

Sounds like it's something in the warmup circuit -- I take it the Jeep drives fine once warmed up, without the problem recurring?

Does it do it if you drive awhile, then go in a store for a few minutes and come out, or just when the engine is cold?

Sounds like it's something in the warmup circuit -- I take it the Jeep drives fine once warmed up, without the problem recurring?

Does it do it if you drive awhile, then go in a store for a few minutes and come out, or just when the engine is cold?

i agree with what he sais and also may be your tps(throttle postion sensor).

Scrapper, you responded to my 'fast idle at startup' post suggesting it could be the TPS. I removed the air intake off the throttle body and disconnected the TPS and, sure enough, normal idle at startup! Plug it back in and, wamo...high idle! Since I don't have a metter to test the voltages, is there any other way to ensure thisis the problem? Can the TPS be cleaned? Also, as I may have stated, I initially thought the problem was the IAC but couldn't figure out why the 'spindle' wasn't moving back and forth ( when IAC removed but connected ) as I turned on the ignition ( without starting )..even on a new IAC! So, I figure the IAC was not getting a signal from the TPS and thus the spindle wouldn't move upon ignition turn-on. Only one thing confuses me....why does idle return to normal after 5-10 minutes of vehicle warm-up?

What say you?

Scrapper, you responded to my 'fast idle at startup' post suggesting it could be the TPS. I removed the air intake off the throttle body and disconnected the TPS and, sure enough, normal idle at startup! Plug it back in and, wamo...high idle! Since I don't have a metter to test the voltages, is there any other way to ensure thisis the problem? Can the TPS be cleaned? Also, as I may have stated, I initially thought the problem was the IAC but couldn't figure out why the 'spindle' wasn't moving back and forth ( when IAC removed but connected ) as I turned on the ignition ( without starting )..even on a new IAC! So, I figure the IAC was not getting a signal from the TPS and thus the spindle wouldn't move upon ignition turn-on. Only one thing confuses me....why does idle return to normal after 5-10 minutes of vehicle warm-up?

What say you? check the i belive the 2 bolts that holds the tps in place and see if bolts are loose if not i'd install a new tps.

I just removed the entire throttle body and the IAC and TPS. Cleaned the heck out of these components. I did check the TPS with my multi-meter and I do get an ohm response when I rotate the TPS, so I assume the TPS continues to function normally.

Put it all back together and the same problem occurs. But here is the latest....

If I disconnect the TPS and start the engine - normal idle RPM! If I connect the TPS soon after startup - engine goes into high idle! However....if I wait to reconnect the TPS until engine is warmed up, then connect the TPS - normal idle RPM!

Also, to answer one of the questions regading whether this high idle occurs at start-up after a short shut off ( e.g. going to a store ), yes...high idle until engine warms up.

So here is the net-net - everything functions as it should after engine warm-up! Absolutely no hesitation during acceleration.

Thoughts?

I think I found the culprit to my high idle at startup ( '93 Wrangler 4.0 )! I know believe the high rpm idle at startup results from a faulty vapor canister solenoid...meaning, the canister is being purged at startup and dumping retained vapors into the ignition. I began to focus on this when I noticed a code of 33 which, at face value, says somthing about A/C clutch control problem ( or something like that ). After a good deal of Internet research, that same code 33 could mean faulty vapor canister solenoid.

Anyt thoughts?