Idle surge from 650-2000 rpm

Hi everyone: I have a 99 C2 that has an idle surge problem. No codes, goes from normal idle up to 2000 rpm, turning the a/c on sort of stabilizes it, but it stays high idle at around 2000. The throttle body is clean, and the m.a.f. sensor is as well. I am dealing with a clutch issue, but this started after that. The threads i looked at did not show the idle going as high as mine. Thanks in advance for any help. Paul

Have you checked if the throttle cable is stuck and have you cleaned the idle control valve?

just a shot here ....but you said you are dealing with a clutch issue....light weight flywheel ? you need to put a pro scan tool on this car and look at the data

Thanks for the replies. Cable is clean and free, cleaned the throttle body and idle control valve, turning the a/c on seems to smooth it out but idle stays way up, removing the oil fill cap seems to effect it (rule out aos),and stock flywheel. Plan on plugging it in to scan on Tuesday. It revs perfectly and smoothly, looked and sprayed for vacuum leaks, none found. Stumped

Recently, having had my TB out, I started the car and had a high idle. I closely checked my TB and saw the throttle cable was holding the TB open so the engine was not returning to idle. Turns out the cable had not fully snapped back in the back of the plastic guide on the TB. I wrapped my fingers around the cable and gave it a tug, heard it snap into the guide and that was it. Simple enough. If your car has a throttle cable, undo it to see if the car idles properly. If so, then check to make sure the throttle cable is fully seated in the guide and is not binding.

I had a similar issue on the pedal end of the cable. I ended up taking the gas pedal apart and greasing things inside. If I recall it was a real PITA to get the gas pedal back together. http://www.renntech.org/forums/topic...al#entry157971

Because it surges on its own I wouldn't imagine it's the peddle or peddle cable - linkage. More like a sensor or vacuum leak but my knowledge is extremely limited in this scenario .

Quotes source post: 12305091

Did you supply power to activate the ICV when cleaning it? Are you sure the internals move freely?

Agree with Ahsai. Leaning towards a problem with the ICV. Did you follow these instructions for cleaning the TB and ICV? http://www.pelicanparts.com/techarti...y_Cleaning.htm The only way to clean the passages for the ICV is to fully remove it from the TB. Is that what you did? Also, are you sure the electrical connector to the ICV is fully seated?

Quotes source post: 12306614

Except that the scenario described by two responders would create a "disagree" between throttle position sensor and actual throttle butterfly position. That could definitely cause a surge.

Update. Now it won't idle at all! It starts, but if I don't put my foot on the peddle to hold it, it dies.

Did you ever scan for diagnostic codes? My idle hunted drastically when I had a bad plug/coil pack. Once I replaced the plugs and coil packs, that smoothed right out. Fuel pump and fuel filter check out? Have you tried running with the MAF disconnected to see if the problem resolves with no MAF?

Mine did that, it was the idle control valve. It was beyond fixing, I have the whole throttle body off another car on mine to get me by while I wait for one from Porsche.

Pulled the throttle body and ICV and cleaned them. The air box was out so the TPS, ICV, and MAF sensors were all disconnected. Throwing no codes which makes no sense. But it was running and surging idling from idle-2000. Used a snap on acanner Thanks for the replies and help, it is appreciated

"surging idling from idle-2000" was that with all TPS, ICV, and MAF disconnected? I'm confused.

Oops, sorry about that. No, surging started out of the blue with everything connected

I second Schnell's reco a few posts above.

Greetings all: Well, I got the other muffler back, and put the other Tubi on, started the car, same issue, starts fine, but will not stay running or idle. No roughness to it. So I held the throttle down to about 1500, revved it a few times, died. Did it again, and now it runs smooth, no more surging, etc... I am stumped, but happy. I did order an ICV anyway. On the Snap On scanner, when I first plugged it in before cleaning the tb or icv, it said closed loop during the surging issue. After cleaning when it would not idle or stay running, it said open loop. Does that give any clues? Thanks again, Paul

Put the new ICV on today. Runs smooth as can be. But.... (there is always a but), my idle is a little higher than past at 800 instead of 650-700. Pulled the oil fill cap off while running, and as predicted, idle drops and runs rough. So, I am not going to worry too much about it. Does it need to "re-learn"? Thanks, Paul

800 is with a/c on or off and it was fully warmed up? Even if it needs to relearn, it shouldn't take too many drive cycles.

A/C off, not warmed up, and when I did turn the A/C on, the idle did go up about 100 rpm. The air pump cycled normally.

Wait till it's fully warmed up then. If it's still not about 700 rpm, check the throttle cable for any binding and make sure the cable is not holding the throttle butterfly open partially.

All is good! Everything back to normal, well.... except for the clutch...... Thanks everyone for your assistance!

[Image-only post; no author-written text. Original image references:] https://rennlist.com/forums/graemlins/thumbup.gif

Erratic engine idle, surging sometimes. 1999 911 C2 996 build date 1/98 Here's the report and fix from shop Light for OBD II (2000-on). Pull codes and freeze frame data. Road test car to get live data from vehicle. Performance check of fuel/ignition management. Run function test for code. Vehicle has codes; P1126- 02 sensing range 1 cylinders 4-6. p0331. Smoke tested for vacuum leaks and found the idle control gasket is bad and leaking. Replace the gasket. Disconnected the battery to reset the idle adaptive. Test dove the vehicle.