Auto Repair Help


by Kyle McFadden

The engine idles too high.

The usual cause of abnormally high idle speeds are vacuum leaks or an inoperative idle speed control motor. A vacuum leak on a fuel injected engine will cause high idle. The oxygen sensor will detect the extra oxygen that is entering the engine through the vacuum leak and will signal the computer the exhaust is lean. The computer in turn will then provide additional fuel which will result in an abnormally high idle.

The first step in the diagnosis is visual inspection. Inspect the throttle cable and linkage for binding. Inspect the engine for vacuum leaks. With the engine at idle, visually inspect each vacuum hose on the vehicle. Listen for a hissing sound which is a key indicator of a vacuum leak. Repair the vacuum hoses as necessary. Inspect the PCV valve and hose. Using pliers, pinch off the hose that supplies the PCV valve. The engine speed should drop slightly. If the engine returns to a normal idle speed, the PCV valve should be replaced. Consult a vehicle specific service manual for location and specific testing procedures. If the vehicle is free from vacuum leaks and the PCV valve is functioning normally, the idle speed control motor or valve may be defective.

You should consult a vehicle specific service manual for proper diagnosis of the system used on your vehicle. Use caution when working around hot or rotating engine parts.

(Kyle has an affinity for Pale Ale and tooling on his 1956 Chevrolet Nomad Station Wagon.)

34 responses to “Diagnose Engine Idles Too High”

  1. glenn says:

    Put new carb kit in boat now it idels really high

  2. john says:

    I have a 2002 nissan sentra 2.5. Rpm idle is high. We already change the throttle body and vacuum is okay also. The tech said my car needs to be reprogram in a computer. Do you think that’s possible?

  3. jay says:

    I have a 1992 chevy s10 that idols extremly high and the second I put it in gear or touch the gas it floods.

    • Bob says:

      Sounds like could be part of the Pollution Control. You have a air compressor that inject air into the exhaust manifold check valve it becomes plugs over time. I had a Camaro it’s 2.8 liter mfi same symptoms change the valve everything worked great be sure to not install it backwards though

  4. adrian wilson says:

    Ive got an 86 toyota supra/ 7MGE / NA IDLES AT 4k rpm any ideas???

  5. Peter says:

    My toyota landcruiser Prado 1990, petrol, 3RZ engine has high idle 1200rpm all the time whether cold or hot. I have changed plugs, fuel filter, oil filter, air cleaner, engine oil but there is no change. I have also noticed the break light coming on and off while driving. I need your help.

  6. Brendan says:

    I too have a chevy s10 it idles fine when its cold, but as soon as its warmed up and hot the idle jumps to 3,000 RPM. I tried to pull out vacuum hoses and see if it changes the idle, It does change abit (higher) then I put it back on and then it slightly goes down, but still 3000RPM and you can really smell the fuel. After I turn it off, I canted start it again for about 20 mins.

  7. Kylie says:

    I have a 1997 Chevy Blazer. It hadn’t moved from our driveway for a year and a half but we finally put a motor in it (used). It has sounded fine since but just yesterday it was idling really high. It hesitates when i start it up and almost shuts off if i dont hit the gas. But when i do, all i can smell is gas.

  8. Chad says:

    I have a Opel corsa lite 1.4, idles extremely high… replaced the ICV, does the same. Cleaned the throttle body, does the same but when i replaced the TPS and disconnected my battery it started to idle normal. 🙂
    #happy days

  9. Welaratne says:

    I have toyota EE102 vagon. recetly i suspect engine idling speed is too high. before get this fault when On the AC engine speed increase and then attched the AC compressor. now revert the other way. engin speed return to nomal when on the AC compressor.

    need your help and recovery TIPs

  10. iain says:

    I have a Honda quad bike 1996 Big Red, and it starts and runs well enough, but the idle grows faster. However if you give it a bit of a shake it returns to idle normally. I have taken the carb out, stripped it right down, cleaned it out, ran air through it, put it all back together and this made no difference to the problem. Do you have any ideas what the problem is?

  11. delphine oliver says:

    i have a 2003 ford taurs an i change the idle control and sensor there is no vacum leaks but it still idole up when i crank it the gas pettle sticks a little and when i press the pettle it takes off by its self

  12. mr. khor kh says:

    my myvi 1.3L manual when first starting the engine while cool, rpm runs high to 1200-1400 till about 10 mibutes when engine hot up, it came down to 800 rpm and becomes normal. Scared this condition may damage the air-cond. Is this so?

  13. Ozman says:

    I have a Diahatsu Terios Kid 2003 model. My car’s RPM automatically got increased recently while i parked the car for a short while. Since then, it is high and reaches at 2.1 in idle. When i switch ON the airconditioner, the RPM reduces to 1.5 and after a short drive when my car’s engine is fully warmed up, RPM fluctuates between 1.5 to 2.2 in a continous rhytm at idle or in stopped position.
    Kindly suggest me what to do and as per your experience what can be the possible malfunction ?

  14. Adrain says:

    Question here guys..
    I have a 1994 oldsmobile 98
    And idk what wrong..when i crank my car it runs but idle high sumtimes in park but in drive it runs most time then it cuts off and some times in drive it will not go faster if giving a lil gas…bought the car from a lady and i cleant the egr valve and pcv valve because my pcv was dirty as idk what….having hard time with this one…sumone help

  15. JERRY says:

    My opel corsa bakkie 2007 model ran out of water hence the water cap of the water bottle was not locked.The was a sound in the engine that sounds like bearings before I poored some water in the waterbottle.I there any damage in the engine?

  16. haleem says:

    I’m new to cars, what’s the average normal range of idle RPM? how to diagnose if ma car’s too high or acceptable-high or normal? I have a 2006 Toyota Corolla, when starting it jumps initially to 2000 then drops to about 1500

  17. Bentley says:

    Why did my tazz idle high and low and when i stop at a stop it die,put a new carburator on but still the same problem.


  19. Jonathan says:

    I have a Corsa lite 1.4i, ive been having problems with high and low idling, i have replaced both my idle valve switches, the problem was still there so i took the car for diagnostic, the diagnostic showed that the sensors where are faulty, they replaced sensors with original parts, the car was fine for about 20mins then the problem came back, somebody please help.

    • Malcolm says:

      Im also have the same problem with my corsa lite 1. 4 Iv tried everthing but to no avail the car still idles high and low when in nutral please help

  20. jacob serugo says:

    i have a suzuki escudo 1994 model idling is very
    low i have changed spark plug and air filter bt no change
    what could be the problem?

  21. Brian says:

    Hello, I have a 1995 S-10 with a 2.2L 4 cylinder engine. Purchase the pickup with a blown head gasket. Tore engine down, reworked and checked head, replaced head gasket and put engine together. Started engine and it has a high idle. 3500 rpm. Checked linkages and they are fine during operation. Looked for vacuum issues but don’t see any. Lots of steam out the tail but o assume that the excess moisture in the crankcase yet.

  22. Stephen says:

    98 Chevy Silverado. Ran fine till this morning it backfired and idled high and cut off. Then struggles to crank but when it does it idles high and then cuts off.

  23. hakyking says:

    pls can anybody help me whit my sienna 1998 model

  24. hakyking says:

    when i move the gear to drive the motor go high speed

  25. Douglas says:

    Where could I locate the valve and the vacuum?

  26. lekoko says:

    I have Toyota corolla 7afe 1997 rev is too high at 2000 what might be the problem

  27. Dexter says:

    I have a 1990 F-150 it will idle around 2300 RPM. Whe. I put it into gear it will drop to a normal idle. I recently have replaced the TPS and the idle air control motor.

  28. AnnMarie Lunetta Milone says:

    83 deville has high idle

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