derekhale

92 SC3 w/ IS3 intake mani. if the accelerator is not depressed the RPMs surge then drop and I want to know what this could be? IAC,TPS,or MAF or something else. Thanks.
Also the high RPM cold start causes some rattling to occur in the engine for about 1-2 seconds then it goes away is that a problem that needs immediate attention?

lemaylexus

Do the revs drop when the engine is warm? SC's do this when they're cold - it's just the engine warming itself up. As for the rattling, I wouldn't worry as long as it goes away quickly. My dad always used to say, "If it ain't broke, don't fix it." I'd just drive it and if you notice anything exceptionally weird then maybe have a mechanic take a look. Otherwise, you should be fine.

derekhale

If I am braking the RPMs drop and surge. If I am at a red light the RPMs drop and surge, sometimes so low the car almost dies then it catches and surges again. This problem just started about a month ago. As long as it is getting some gas it holds RPMs just fine it is only when the gas pedal is not depressed that it does this.

Johnny3

Believe this or not: Check your coolant level while engine is cold, top it off & see if that changes anything. It can cause the surging.

qmanlexus2

As Far as the surging it might be your Battery ground cable is erroded. Buy a Ever start Neg Battery cable 15" 4 Gauge from Walmart for 7 to 8 Bucks and connect it to bottom ground bolt. Follow the cable down and you will see it. Leave the excisting cable hang. I think the surge is happening everytime you hit the brakes. This is a Inexpence fix and it got rid of all my electrical gremlins that I was having. Let me know if it works

scfou

iTrader: (3)

How about a faulty throttle position sensor?

scfou

iTrader: (3)

Maa bad.. doesn't sound like the TPS. This is a bad AFM/MAF. Just replace the black box and that should do the trick. I had to do the same thing before. If you down shift before the stop this will prevent you from having to tap the throttle to hold the idle, Lol.. But if you floor the pedal and come to a sudden stop it'll die.

djrazr

iTrader: (2)

I kinda get the same thing and don't know what it is. It only happens on cold starts. The engine will rumble on and off at around 1800 rpms, just up and down, some shaking then smoothing out. This goes back and fourth. Once the engine is warm, this goes completely away

Have no idea what it is

miraluna

iTrader: (2)

did you guys fix the problem?

djrazr

iTrader: (2)

Nope...it seems nobody here knows the answer. Lots of views but no replies

grindin8o8

could be a lot of problems. i suggest you buy a ohm meter and test your idle air control valve and maf sensor. if they both work fine, try cleaning the idle air control valve and replace the bearings. if still have the same problem, buy a new used ecu.

sc-driver

iTrader: (7)

make sure ground connections are good, battery connections are good.... Like said, check IACV, check maf, most importantly check for vacuum leaks.

Once you've done that, seafoam the car through the pcv or brake booster and reset the ecu. This should reduce you surging a little bit.