Do Not Sell My Personal Information Jump to content

Idle Speed Surging Up And Down Help


Recommended Posts

:cries: Idle Speed surging up and down HELP

I had my car serviced at a car wash. Lube, Oil, and Filter. They told me the Air cleaner was dirty so I had them put a new one in. When I got the car back, the idle was going nuts. Car starts fine, but idle never goes below 1,100 rpm, and goes straight up to 2,100, then right back to 1,100, and back to 2,100…. And it keeps doing it. Wither the car is hot or cold. Car runs fine on the road, but will not go below the 1,100 rpm. I have researched the posts but found no help. I did check vacuum lines. Can’t find any loose ones. Can’t find any vacuum leaks. I tried “taping” on the Mass Airflow Sensor, the throttle body and so on. All to no help. I did find out that before they gave the car back to me they forgot to plug the connector back into the Mass Airflow Sensor before starting the car, but then plugged it in. I also found out they “Spilled” oil on the engine so the washed it of with engine cleaner and low pressure water. Help… I do not have a clue as to what to do. Car wash guys say nothing they did caused this. But car was fine when I drove in. Help. Thank You.


Link to comment
Share on other sites

always do your own oil changes..........and thats exactly why, those guys are incompentent (sp) idiots that work at those places

if the maf was disconected and the car was started, you need to disconnect the battery for about 10 minutes and let it reset itself.

so you did check the vaccum lines, check them again, that is a very common solution to those symptoms. they might have broke the return line that runs to the intake assembly.

also when was the last time you had a tune-up? you could have a fouled plug or a crack ignition wire, get a tester and read the resistance of the wires.

when u washed the engine, did you cover up all electrical? ie...... dist cap ect..........


f not that probably is the problem, you might have shorted out something in there with the water.

did you put a low pressure water hose on it?

for future reference don't ever put a low pressure water hose on your engine bay, if you have to do that use a high pressure sprayer, and make sure you cover up all electrical.

Link to comment
Share on other sites

Still No Go!

I took the + terminal off the battery for well over 10 minutes. In that time I again looked for vacuum leaks etc. I found the hose clamps by the Air sensor slightly loose. I tightened them up. I found no other air or vacuum leaks, lose wires connectors etc. I hooked the battery back up, and started the car. For about 40 seconds it idled steady at about 1,100 rpm (outside temp about 70 degrees) Then it started surging again. Up to 1,800 rpm, then down to 1,100 rpm, and so on. I turned it off. Restarted and the surging was immediate. Hitting the throttle was of no help!!!

Any other ideas???? I was going to drive the car into Los Ageless today but have doubts about taking a 400 mile drive in it. Any thoughts on driving it a long distance like this? Anyway, I'm taking my 84 Saab to L.A. instead. I just hate taking it to L.A., it is in amost showroom condition, and I hate what L.A. folks do to other cars. When I get back in a few days I'll deal with this. I'm about 100 miles from Las Vegas and about 50 miles from Lake Havasu if anyone knows a good independent mechanic in either of those two cites please let me know. The car has just over 100,000 miles on it. Had last major service by a dealer in L.A. at 60,000 miles. I'll check back in on any new info. Thanks.

Link to comment
Share on other sites

I had the same problem about 9 months ago. The cause of the problem is the "idle speed control valve". A very expensive part, about 600.00 to 800.00. Or hopefully you know a very good mechanic that can adjust the valve and just charge you for labor like he did for me. Also might as well clean out the throttle body while your at it.

Link to comment
Share on other sites

WhenI put it in gear and foot on the brake the egine is at abot 1,000 rpm. If I take my foot off and let the car go, it will go up to 1,500 rpm and stay there. Is this valve known to just go out of wack like this????

Link to comment
Share on other sites

Holy mother - Alldata lists the ISC (Idle Speed Control) for 1991 LS 400 at $694 for parts and an hour of labor. Bad news is that the idle speed is controlled by the computer. Kind of a guess as to which is the culprit, but I would assume the ISC is sticking, which would account for the ups and downs. Just my uneducated guess. Good news is that the car shouldn't be affected while driving as the ISC just provides a bypass of your throttle body which would be closed when your foot isn't on the gas. I might not use the A/C, but you can try it and see what happens around home first.

My sympathies, and good luck.

Link to comment
Share on other sites

  • 2 weeks later...

:pirate: I found out my idle surging was in fact a bad Idle Control Valve. The unit is dead, and will not even move when jumpers are put on it. Looks like it just dead on it's own. No sign of water getting to it. The mechanic says he can order one for $725.00! O.K. I found one online for $600.00, but come on! What is in this thing that they are charging $600.00! I can buy one hell of a nice TV for less, or a great digital SLR camera!……

Any suggestions on saving on this? I can’t really go without fixing it.. I have two other cars, so the Lexus will sit till I decide what to do.

Also I need new plugs and wires. Water did mess up the plugs and wires. The car has 116,000 miles on it. Last tune up etc., was at 60,000 miles. Any thoughts on if I should replace the “distributor” caps also (they look ok). And the timing belt????

Open to any and all thoughts. Thank you.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...