idle surge then die, help!

[eric90lx]

Tonight my car just started having a random problem where at idle it will drop the idle really far down like 300rpm then shoot up then repeat until it would die, also has a hard time starting sometimes unless unless I give it some throttle. Hope you guys can help me rectify this issue.

Thanks, Eric

[BradM]

What car/engine?

[eric90lx]

1990 5.0

[Sleeper]

Run the codes?

I always started with cleaning the maff with cleaner and then a simple pull the battery and reset.

[eric90lx]

For some reason my car doesnt pop up check engine codes the previous owner must of rigged it up some how.

[JC316]

+1 to the MAF. I would also look hard at the IAC valve.

[Baba Ganoush]

Clean your mass air sensor and idle air bypass sensor, then do a Reset Base Idle procedure.

http://sbftech.com/index.php/topic,1031.0.html

[TX21]

My car does that same crap. Going to re-set the idle today.

[eric90lx]

Still need help trying to solve this, I cleaned my mass air, throttle body and replaced iac, still didnt fix it. Then I tried a new ignition coil and checked cap and rotor and new spark plugs, still didnt fix it. I have a tps sensor im about to throw on there tomorrow but any suggestions you can can give me would be very helpful. Its pretty bad I cant even slow down to a stop because any times I have the rpms below 1500 it will do it so shifting gears, slowing down, etc.. when I push in the clutch it like bucks and jerks the car too.

[Sleeper]

Test all sensors you can and clean the grounds.

If you know any of your buddies that can let you borrow a ecu just for the heck of trying it.

[eric90lx]

How do you test the sensors?

[Baba Ganoush]

Did you reset the idle?

Also, clean the main wire harness connectors behind the intake (salt and pepper shakers) and add dielectric grease.

[Denny]

I was having the same issue with my Mark VII. I cleaned the TB, then did the idle reset like stated in the link. All is well now. TPS was sitting at .92.

[Denny]

Still need help trying to solve this, I cleaned my mass air, throttle body and replaced iac, still didnt fix it. Then I tried a new ignition coil and checked cap and rotor and new spark plugs, still didnt fix it. I have a tps sensor im about to throw on there tomorrow but any suggestions you can can give me would be very helpful. Its pretty bad I cant even slow down to a stop because any times I have the rpms below 1500 it will do it so shifting gears, slowing down, etc.. when I push in the clutch it like bucks and jerks the car too.

You probably didn't need to replace sensors. Did you follow the steps in the link? It's important to do it like it stated. After cleaning the TB, idle it. If it struggles, idle it up with the positioning screw under the TB until it can stay steady. While it's idling, unplug the IAC. It will most likely die. Fire it back up and try to keep it going with the IAC unplugged. Reconnect the iac and try it again, this time, idle it down as far as it can go, trying to hit between 600-800 RPM. Kill the car, then turn it on with just the ignition on but not running. Test the TPS wih a volt meter. Have it set to roughly 10-20 on the DC voltage setting. Push the positive probe into the green TPS wire and the negative into the black wire. If you're reading is .8 - 1.0, you're good on the TPS. Disconnect the battery for a few minutes and let the comp reset. Reconnect and fire it back up. Hopefully, that takes care of it. It might be slightly surging at first, but let it figure it out (usually less than 3-4 minutes). If it seems better, drive it around for 15 minutes.

Also, if you're still having troubles after you do the above AND replace all those sensors, you might also look into a vacuum leak. I hunt for those best by letting I tilde and spraying carb cleaner around the vacuum lines until I hear a variance in RPMs. Those old vacuum lines do get brittle.

[Lone Star Performance]

He did a compression test and found 0 compression in #1. All others were around 145