My car has been running at idle in park between 1000-1300 RPM. I cant find any vacuum leaks. Where else to look? I bought the car w/ the AC already removed. Would that cause this problem? Im new to TPIs so looking for a bit of help. There are no check engine light on. The air box is also plugged off. Im thinking that may be athe problem. The manual I have show no vacuum diagram. Any inf would be great. Thanks

Its possible the AC delete did this... Im not saying for sure..BUT there is a loop in the ECM that bumps up the idle via the iac valve when the AC kicks on.. that way the load of the AC does not stall the vehice...

Anyway I remember when deleting my AC I had to pull my harness and find a Ground wire***had a ring on it and everything>>I think it was a Blue wire***Its been years but Im pretty sure it was blue... I had to ground that to defeat the high idle...

However I dont remember it kicking up that high.. Id probably remove the TB and clean the IAC ports and reset the IAC... Also loo at the back side of the TB.. where the throttle plate is..Youll see a screw that adjusts the butterfly....Look where the head of that screw should be on the backside....IF there is a PLUG there then you should be good.. IF the plug is gone and you can see the torx head that means someone has MESSED with it in the past.. IF that is the case Look in the archives or tech help section for MIN AIR adjustment procedure and IAC reset procedure>>>Also when messing with MIN air you must reset the TPS voltage..


Sorry if this does not make sense... If you need me to elaborate then PM me... Im adduming you know what TPS, IAC TB etc all mean..


And finally what do you mean the air box is blocked off??

1000-1300 RPM in park is normal for my car, but mines only a 305, so it could be different.

1000 Id buy in park...But 1300 seems high..

Another question... IF you put it into gear... And JUst keep you foot off the gas and foot on the brake... what RPMS do you read>>>

I understand what you mean. The airbox has a wood doule stuck in one of the ports, blocking it off. W/O having a vacuum diagram to follow Im not 100% sure where the lines should and should not go.

The car runs great except for the high idle. When the car is in gear it wants to pull throught the brakes. I have to hold the pedal down real hard to keep it stopped.

Im not the greatest mechanic but I know this is not normal.

500 rpm's

Depend how high they were in park. Its speratic, it usually somewhere between 1000-1300. In gear and foot on the brake there usually never below 700. But w/ will happen is after I take my foot off the brake the car obiviously rolls on idle but the spped of the car increases. It will acutally shift into second and roll the car about 25 MPH.

I would check the throttlebody idle adjust screw... shoulkd take 2 seconds just to look and see if the blockoff was removed..usually if you buy a car previously owned by an OLD SCHOOLER it will have been INCORRECTLY REMOVED AND ADJUSTED to cure and idle problem...which is wrong... ANOTHER thing to check that Ive seen happen is check the adjustment on the cruise control cable... Ive see a waaayyy out of adjustment cable actually hold the throttle plates open...

IF you see the idle adjust screw has been messed with then find the article o n MIN AIR RESET... I had to do this to my vette which had a similar issue...

The cruise doesnt work, thats why Im gussing its a vacuum problem since the cruise work off vacuum. Correct me if Im wrong.

I removed my cruise in like 1997 so forgive me if Im wrong....But I dont recall it running on vacuum.. I thought it was an electrical servo... and relied on feedback on vss...

As for the routing diagram, this should be close:

Thanks for the diagram Vader. I havent gone into the C/C yet but I had an 89 Blazer which was TBI and the C/C ran off vaccuum. I know its a totally different setup, but I figured it might be the same.

The '87 should have a vacuum operated cruise servo. The supply for the cruise is shared with the HVAC control vacuum supply. While a vacuum leak can cause a higher idle, the HVAC supply port is not large enough to cause a leak sufficient to raise idle that much.

Other potential vacuum leaks which might be large enough are the PCV valve, EGR valve, and brake power booster.

Of course, these should all be checked AFTER verifying that the throttle body is clean, the throttle shaft and cables are not binding, and the minimum air position (throttle stop screw) is set correctly.

Idle for the V8 cars is "supposed" to be 400-450, according to the service manual, but the prom has a target idle of 575.

My car sometimes gets stuck in a high idle (1000-1200) when it's cold and the car is warmed up or when I drive the car really hard.
shutting down and restarting the car resets the idle back down to 650-750.

the 400-450 is for setting MIN AIR... As in IAC unhooked so the ecm can not influence incoming air... and the throttle blades closed to achieve 400-450 with the engine at operating temp...

Then when you hook the iac back up it will raise it back to the 575+ rating


Vader you have me thinking hard on this one.. Now youve forced me into going home tonight and pulling the box with my cruise control out... I seriously dont remember seeing any vacuum lines going to the CC..

Did your CC look like this one?


this is the only pic I have of my stock engine showing the Cruise.

EDIT: found a couple more, Looks like 2 vacuum lines go to it.

I have been discussing this same problem on another thread here ---> http://www.thirdgen.org/techboard/te...-problems.html (IDLE Problems) mine started off with super high idle in park, then in gear.. I replaced the IAC and set min air to 450 RPM and TPS to .54 and it worked fine for awhile, but after almost a week i got a code for TPS voltage too low. so I replaced the Throttle Position Sensor and connector, again my car idled fine for almost a week but now I still get that code for low TPS voltage, when I read it with my auto xray it's set to .54 with Key On Engine Off, then while running voltage bumps up to .56 and when the code throws (usually on the freeway) the voltage drops down way low to 0.05-0.09 but it still goes up when accelerating just only up to maybe 1 volt.. I noticed the coolant temp and intake air temp sensors share ground so I cleaned up and checked the wiring seems ok. I am thinkin maybe bad ECM or somethin funny. air intake blocked off doesn't sound very good!! you still have air comming thru the filter into the engine right?? i would really sugest a scan tool if you don't have one. they are kind of expensive but so is a mechanic! you can use jumper wires to check TPS voltage but it's kind of a pain. but with the scan tool you can see TPS voltage and IAC counts plus ton of other stuff.