Idle problem after disconnecting battery

[tito12121]

Hoping someone can help.

I know idle problems have been documented thoroughly and ive read through many threads on many forums but I have a very specific issue.

I got my car in November and it had a jumpy idle. I got a replacement ICV Bosch unit from a member on here. It fixed the jumpiness but was still a little rough. I got new timing belt and all the goodies that go with it, new Bosch o2 sensor and ran some Lucas Injector cleaner (tune up in bottle) and my idle problem has been gone for months since Feb, car running very smooth idling around 800 no jumps whatsoever. On cold starts it revs at 1500-2k and starts coming down until the engine heats up, im assuming thats normal.

Today I installed the remote door opener so I had to disconnect my battery, Once i reconnected and started the car It was idling low 500 and jumping 500-800 and if I hit the gas on Neutral it would die out after.

What did I reset or change by disconnecting my battery? Is there some type of specific way to reset my ECU or Idle again? Im hoping it will just go away on its own next time I drive it but if not what should I check?

[Maddog]

You will need to drive the car for a bit to refresh the ECU.

[tito12121]

when i first had the idle problem I played with that little set screw thats attached to the accel cable. not sure if that messed with it too. Ive driven it a little, seems a little better but still does not start high and drop from a cold start

[squidmaster]

Assuming you're in an e30 with stock(ish) M20 or M42, 800rpm is a high idle. Adjusting the throttle tension may have left the throttle butterfly valve open more than normal, giving the ECU a different learned fuel trim or idle adjustment. Resetting the ECU has undone any of the adjustments that were made before. If you need to adjust idle, adjust it using the ICV screw or the throttle plate stopping screw (do that as a last resort). Hopefully your car will relearn the corrections made, but if not I would go in for a smoke and compression test.

[squidmaster]

Your car should idle fine with slack in the throttle cable. If it doesn't then adjustment needs to be made elsewhere.

[tito12121]

Assuming you're in an e30 with stock(ish) M20 or M42, 800rpm is a high idle. Adjusting the throttle tension may have left the throttle butterfly valve open more than normal, giving the ECU a different learned fuel trim or idle adjustment. Resetting the ECU has undone any of the adjustments that were made before. If you need to adjust idle, adjust it using the ICV screw or the throttle plate stopping screw (do that as a last resort). Hopefully your car will relearn the corrections made, but if not I would go in for a smoke and compression test.

Completely stock M20. Im going to take pictures tomorrow. Honestly im not really mechanically inclined so I dont know if I adjusted throttle tension or throttle plate stoping screw. I just hope to get back to normal before I install E36 Injectors and a chip.

[squidmaster]

The thing I always recommend to people is to have a properly running car FIRST, then modify and tune. Adding modifications and a tune to a car that isn't working correctly will only exacerbate the issues and make it harder to track down the causes.

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[dnguyen1963]

Completely stock M20. Im going to take pictures tomorrow. Honestly im not really mechanically inclined so I dont know if I adjusted throttle tension or throttle plate stoping screw. I just hope to get back to normal before I install E36 Injectors and a chip.

Lofty goal! I suggest that you get to know your car really well before doing any mods.

[Cephas]

You will need to drive the car for a bit to refresh the ECU.

This. Each time you disconnect the battery you will get a strange idle and rough running for a bit. Take it for a drive and warm the engine entirely. Should sort itself out.

[Cephas]

You will need to drive the car for a bit to refresh the ECU.

This. Each time you disconnect the battery you will get a strange idle and rough running for a bit. Take it for a drive let the engine get to operating temp. Should sort itself out.

[tito12121]

Lofty goal! I suggest that you get to know your car really well before doing any mods.

LOL I know thats the logical thing to do, Ive been reading on here for months so I'm sooo eager to do all the cool little things I've been reading about. Luckily I dont count on this car to get around so I dont mind taking some minor risks and do the easier DIY mods as long as they arent too detrimental. Long term super lofty goals are engine and 5 speed swap, not to be carried out by me of course, i'll just source parts.

This. Each time you disconnect the battery you will get a strange idle and rough running for a bit. Take it for a drive and warm the engine entirely. Should sort itself out.

It has smoothened out a bit so I'm happier but I still feel it may not be at its optimal position, I read on another post how to properly adjust the stop screw and tps with ICV disconnected. Will try this over the weekend.