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RIP
RIP, Lead Technician
Category: Car
Satisfied Customers: 5591
Experience:  A.S.E. Master Technician, Advanced Level, Smog - European, Domestic, & Asian -- Car Category Mentor
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my idle air control valve on my 95 chevy pickup

Customer Question

my idle air control valve on my 95 chevy pickup is not working. i put a new one in but it did not work.it is all so not shifting right i have to run the rpms real high to make it shift the higher the gear the high the rpm .it was all fine and yesterday i washed under the hood with the garden hose then it started. what is wrong
Submitted: 6 years ago.
Category: Car
Expert:  RIP replied 6 years ago.

Hi, welcome to Just Answer.

  1. Has the check enigne lamp come on when this began?
  2. Did this all begin immediatly after the engine was washed?
  3. Does the engine idle low, high, or not at all when the truck is in park/neutral?
Customer: replied 6 years ago.
no it didnt come on. yes as soon as i got done washing it. 2200 rpms
Expert:  RIP replied 6 years ago.
Thanks, XXXXX XXXXX like water intrusion is causing the problem(s)...but where is the question. There are various placed water can get in if the seals to electrical connections are weak. The first step is to spray WD-40 (Water Displacement 40) on the entire engine bay, paying close attention to the electrical connections. If you have access to compressed air, it would be a good idea to spread/dry the bay with compressed air after the WD-40 application. There is a chance the WD-40 will enter an area and clear the moisture. If the truck still acts up, than you'll individually need to disconenct the electrical connections and spray WD-40 in there and air dry them, until you find the cause. The first connector to do this to is the engine computer, since it has the largest impact on both of these conditions. Let me know if you have trouble locating the computer.
RIP, Lead Technician
Category: Car
Satisfied Customers: 5591
Experience: A.S.E. Master Technician, Advanced Level, Smog - European, Domestic, & Asian -- Car Category Mentor
RIP and 12 other Car Specialists are ready to help you
Customer: replied 6 years ago.
Reply to RIP's Post: the ecm is under the glove box how would that get wet
Expert:  RIP replied 6 years ago.
Sorry your correct, yours has a ECM (Engine Control Module), later models had the VCM (Vehicle Control Module) which is mounted under the hood on the driver side. Spray WD-40 on the electrical connections and wiring under the hood and if the problem persists, check for any water intrusion to the TPS, IAC, ECT, and the MAP. Also disconenct the throtle cable from the TBI to be sure the cable isn't binding and causing the higher idle, which can affect shifting. Try disconecting the battery cable for 30-40 seconds to clear the ECM in case after replacing any of the parts you mentioned, the ECM is running off predetermined values. Also, be sure the cables are tight on the battery, especially the positive cables. Let me know if you are still have a high idle concern..
Customer: replied 6 years ago.
yes it is still hard to stiff and idleing high.
Expert:  RIP replied 6 years ago.

Hmmm, I can't think of anything else at the moment, possibly letting the engine bay dry out with the hood open, may do the trick. But let me 'opt out' of the question so if any other GM Experts here have ran into this before, they can offer their advice as well...hang in there other Experts will look through the question throughout the rest of the day. If I come up with anything else, I'll post back here.

 

Customer: replied 6 years ago.
thanks
Expert:  Shawn replied 6 years ago.

grassman,

Dry out the underhood fuse box and check fuses ENG 1, ECM 1 and ECM B.

Had this happen to my car and ENG 1 fuse blew.

 

 

 

Shawn

Customer: replied 6 years ago.
already did that nothing happened
Customer: replied 6 years ago.
Reply to RIP's Post: im getting power to the plug at the iac. to two of the four wires the other two i guess are ground wires. when i disconnect it the check engine light does not come on nor does the engine change at all. when i unplug the map or tps the truck goes right into limp mode the check engine light comes on and it slows rpms. i connected the iac plug to another iac motor that i bought it moved out a little bit but did nothing else i let sit there for a minute and it didnt move i hit the gas it didnt move.but there is 14 volts at the plug and i have two brand new sensors from different companies.the same with both. i can pull the pintle out on the iac and put it back in and it will hold a good idle until i drive it or start revving the engine. im clueless does any of that help you thanx for helpin me i will accept your aswner but i was not sure if i could still talk to u if i did thanx brian
Expert:  RIP replied 6 years ago.

Disconnecting the IAC valve will typically not set the check engine lamp. It's very unusual that after washing the engine you could actually short an electrical circuit out, so the problem must still lie in water intrusion or a blown fuse as the other Expert mentioned; unless this condition is entirely coincidental and the ECU has failed...which would be too coincidental. Unfortunalty at this point the IAC circuit needs to be tested with factory equipment, unless the problem can rectify itself. I can offer you the factory procedures for testing below to see if anything can further help you issolate this. Than I can opt back out of the question and other Experts will continue to look through this and see if there is any that have run accross this. In my experience a high idle is commonly due to a binding throtle, a vacuum leak, a bad IAC, or a bad ECU...possibly a vacuum leak was produced when the enigne was cleaned??

graphic

graphic

CIRCUIT DESCRIPTION
The control module controls engine idle speed with the IAC valve. To increase idle speed, the control module retracts the IAC valve pintle away from it's seat, allowing more air to pass by the throttle bore. To decrease idle speed, it extends the IAC valve pintle towards it's seat, reducing bypass air flow. A Tech 1 scan tool will read the control module commands to the IAC valve in counts. Higher the counts indicate more air bypass (higher idle). The lower the counts indicate less air is allowed to bypass (lower idle).

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

  1. The IAC tester is used to extend and retract the IAC valve. Valve movement is verified by an engine speed change. If no change in engine speed occurs, the valve can be retested when removed from the throttle body.
  2. This step checks the quality of the IAC movement in Step 1. Between 700 rpm and about 1500 rpm the engine speed should change smoothly with each flash of the tester light in both extend and retract. If the IAC valve is retracted beyond the control range (about 1500 rpm), it may take many flashes in the extend position before engine speed will begin to drop. This is normal on certain engines, fully extending IAC may cause engine stall. This may be normal.
  3. Steps 1 and 2 verified proper IAC valve operation while this step checks the IAC circuits. Each lamp on the node light should flash red and green while the IAC valve is cycled. While the sequence of color is not important if either light is "OFF" or does not flash red and green, check the circuits for faults beginning with poor terminal contacts.

IAC VALVE RESET PROCEDURE

  • Disconnect battery cable at battery for 10 seconds then reconnect cable.
  • Ignition "ON," engine "OFF" for 5 seconds.
  • Ignition "OFF" for 10 seconds.

DIAGNOSTIC AIDS
A slow, unstable, or fast idle may be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Out of control range, IAC Tech 1 scan tool counts will be above 60 if idle is too low, and zero counts if idle is too high. The following checks should be made to repair a non-IAC system problem.

  • VACUUM LEAK (High Idle) - If idle is too high, stop the engine. Fully extend (low) IAC with tester. Start engine. If idle speed is above 800 rpm, locate and correct vacuum leak including crankcase ventilation system. Also, check for binding of throttle blade or linkage.
  • SYSTEM TOO RICH (Low Air/Fuel Ratio) - The idle speed will be too low. Tech 1 scan tool IAC counts will usually be above 80. System is obviously rich and may exhibit black smoke in exhaust. Tech 1 scan tool O2 voltage will be fixed above 800 mV (0.8 volt). Check for high fuel pressure, leaking or sticking injector. Silicone contaminated O2S scan voltage will be slow to respond.
  • THROTTLE BODY - Remove IAC valve and inspect bore for foreign material.
  • IAC VALVE ELECTRICAL CONNECTIONS - IAC valve connections should be carefully checked for proper contact.
  • CRANKCASE VENTILATION VALVE - An incorrect or faulty crankcase ventilation valve may result in an incorrect idle speed. Refer to Diagnosis By Symptom / Rough, Unstable Or Incorrect Idle, Stalling .
  • A/C COMPRESSOR - Refer to A/C diagnosis if circuit is shorted to ground. If the relay is faulty, an idle problem may exist. Refer to Diagnosis By Symptom / Rough, Unstable Or Incorrect Idle, Stalling .
  • If intermittent poor driveablity or idle symptoms are resolved by disconnecting the IAC, carefully recheck connections, valve terminal resistance or replace IAC.

 

 

Customer: replied 6 years ago.
Reply to RIP's Post: vacuum leak would affect idle at all times right i have had the truck idleing for two hours at 700 rpms with no change but i pull the pintle out by hand before i put it in and i have not touched the gas. i would notice a vacuum leak right. could i have fried the pcm when wet the wires and it only burned out certain parts. i pulled out the pcm and it looked and smelled fine no burnt smell i blew it off with with the air comprsser i looked at the prom i looked fine.
Expert:  RIP replied 6 years ago.
You may or may not notice a vacuum leak, since the IAC is trying to compensate; and typically when you pull the pintle out by hand and plug in the connector, once the key is turned on the IAC resets to where the computer wants it to be. And it would be very rare to short any component out unless you actually got water inside of it, so if it isn't a vacuum leak or water intrusion...the best bet is to test the system according to the factory procedures requiring an IAC driver, or tester through a factory level scan tool. By going through the flow of diagnostics, the problem will definitly be discovered. Remember to try and disconnect the battery cables, as the myself and the procedures recommend, becuase if there was a problem and now it's fixed the computer will continue to use the parameters it has learned, by disconencting the battery cables, those parameters are reset.
Customer: replied 6 years ago.
as soon as i unplugged the sencor while the truck was still idleing at 700 it shut off as soon as i started it the idle is high and it still shifts only over 3000 rpms any last suggestions before i get raped for countless hours of wiring diagnostics that i already performed
Expert:  RIP replied 6 years ago.

Hmmm, that sure does sound internal to the ECU, but it's hard to say without proof. Just go ahead and keep the post open, we have a great staff of GM Experts and another may have run across a similar problem.

Sorry, sometimes it's difficult to interpret what going on without having my hands in the car, unless I've experienced an identical occurrence.

Customer: replied 6 years ago.
i know i have been doing this since i was little and im stumped i owned an 87 dodge aires i know about water intrudion that thing stoprunnin everytime i it a poodle but a little wd a few hours to dry it ran.with both the iac and the trans acting like that i think it got the pcm. one last thing the trans not shiftig unless i bring it to 3000 or 3500 rpms be fore it shifts is that the shift solnoids or the range mode selector
Expert:  RIP replied 6 years ago.
Was the trans doing this before the wash? If not, than it must be due to the high idle. If the idle isn't correct the ECU will calculate the shifts incorrectly as well as the mechanical throttle valve will not open and close properly. But, there is a possibility it's the ECU not shifting the transmission correctly. Man if you can get your hands on a factory level scan tool, like a second hand Snap-On on eBay (with updated cartridges), we can test the idle and see when the computer actuates the shift solenoids.
Customer: replied 6 years ago.
i can get a snap on computer i just ordered a new pcm for 70.oo bucks after this i think im goin to tke it to the shop

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