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Jphoenix13

Off-idle stumble

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I have a slight hesitation coming off idle with my 95 S4, worse when cold. I've read through the posts here about how the IAC affects idle and hesitation when starting out. It seems better when warm, but still needs more throttle than I would expect when starting off in first.

 

I loaded up two logs, part 1 is from cold start to halfway up to 80° - file is too large to load up all at once. Second half of the warmup is in the second post to get around the 1mb file post limit.

 

The IAC does not come down below mid 50's after it reaches 80°. I shut it off when coolant temp reached 83°.

 

Your thoughts, comments and recommendations greatly appreciated.

 

Jim



I guess I can't load part two because it exceeds the file size limits for upload. The .csv file is 1.2mb, I tried cutting out the uninteresting parts, but could not get it below 1mb. Seems it takes too long for the car to warm up to 80°!



You can download the entire .csv log here: http://www.jimphoenix.com/2013/05/lotus-ecu-log/

 

Thanks,

 

Jim

Edited by Jphoenix13

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Resolved!

 

I got the S4 warm, adjusted the IAC down to about 30 and now it runs very nice. No more off-idle stumble, pulls away from a dead stop perfectly. Much better behaved than before.

 

 

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:thumbsup:

 

Excellent news and welcome to TLF :D

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Resolved!

 

I got the S4 warm, adjusted the IAC down to about 30 and now it runs very nice. No more off-idle stumble, pulls away from a dead stop perfectly. Much better behaved than before.

How did you adjust the IAC valve?  Internally?  

 

Or do you mean that you adjusted the throttle stop until the IAC closed itself down to 30?

 

I've a similar stumble off idle, but no freescan to work with.  If the throttle stop, would you say you turned it a half turn or so?

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Richard,

 

There is a procedure for adjusting the minimum air rate bleed screw while monitoring the IAC stepper motor counts, using Freescan or Espritmon (or a Tech1 with the lotus cartridge).

 

Do not try to adjust the screws on the throttle butterflies without out following the procedure or without using the scan tool!

 

If you try to adjust the idle, the ECu will fight everything you do, and it is very easy to get out of range really quick, and cause a poor drivability condition.

 

The IAC counts must be between 20-40 when the engine is fully warm at idle. The minimum air rate bleed screw is turned tiny tiny amounts in order to achieve this 20-40 IAC value with long pauses to wait for the reading to stabilize.  The amounts that you turn the screw are nearly imperceptible, and can cause large changes.

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Richard,

 

There is a procedure for adjusting the minimum air rate bleed screw while monitoring the IAC stepper motor counts, using Freescan or Espritmon (or a Tech1 with the lotus cartridge).

 

Do not try to adjust the screws on the throttle butterflies without out following the procedure or without using the scan tool!

 

If you try to adjust the idle, the ECu will fight everything you do, and it is very easy to get out of range really quick, and cause a poor drivability condition.

 

The IAC counts must be between 20-40 when the engine is fully warm at idle. The minimum air rate bleed screw is turned tiny tiny amounts in order to achieve this 20-40 IAC value with long pauses to wait for the reading to stabilize.  The amounts that you turn the screw are nearly imperceptible, and can cause large changes.

Yes, mine was sitting around 70 or so when warm (after a climb up the hill and home, so it was sitting around 85C). A small adjustment to the min air rate bleed screw resulted in immediate drop to 40 to 50 on freescan. Then another drive and it stabilized around 30 to 35, I'm happy with that.

 

Now I think my injectors need cleaning or replacing, the car has 38,000 miles and while it idles OK, it rambles a bit at idle, from 970 to 990. No problems under power at all, just the typical barely perceptible hesitation form a dead stop. Much better than before, but I read somewhere the injectors are only good for 40k?

 

I've been reading the various injector threads, I'd like to replace them with OEM, any sources in the states people like?

 

There's a company in Seattle that cleans them with a 5 day turn, but then I'd have to wait for winter as this car has become my DD now ;-)

 

Jim

Edited by Jphoenix13

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Richard,

 

There is a procedure for adjusting the minimum air rate bleed screw while monitoring the IAC stepper motor counts, using Freescan or Espritmon (or a Tech1 with the lotus cartridge).

 

Do not try to adjust the screws on the throttle butterflies without out following the procedure or without using the scan tool!

 

If you try to adjust the idle, the ECu will fight everything you do, and it is very easy to get out of range really quick, and cause a poor drivability condition.

 

The IAC counts must be between 20-40 when the engine is fully warm at idle. The minimum air rate bleed screw is turned tiny tiny amounts in order to achieve this 20-40 IAC value with long pauses to wait for the reading to stabilize.  The amounts that you turn the screw are nearly imperceptible, and can cause large changes.

The "minimum air rate bleed screw", where is this?  Or do you mean the adjustment screw that just holds the butterflies open?

 

I gave the butterflies adjustment a 1/4 turn open and other than a high cold idle to start with, the ECU figured it out pretty quick and all seems well.  I'm not sure this solved my problem though.  The car still seems hesitant in that instant when you first apply gas and begin releasing the clutch to get moving.  Perhaps I'm just driving too conservatively and need to rev her up a bit more before releasing the clutch!

 

I will get myself a cable and try to figure out this laptop thing one day.  But for a non computer guy, your discussions of ports and configurations and adapters are quite intimidating!  lol.    

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The "minimum air rate bleed screw", where is this?  Or do you mean the adjustment screw that just holds the butterflies open?

 

I gave the butterflies adjustment a 1/4 turn open and other than a high cold idle to start with, the ECU figured it out pretty quick and all seems well.  I'm not sure this solved my problem though.  The car still seems hesitant in that instant when you first apply gas and begin releasing the clutch to get moving.  Perhaps I'm just driving too conservatively and need to rev her up a bit more before releasing the clutch!

 

I will get myself a cable and try to figure out this laptop thing one day.  But for a non computer guy, your discussions of ports and configurations and adapters are quite intimidating!  lol.    

 

Richard,

 

There are 2 adjustment screws on the butterflies.  One should never be touched! and the other should only be adjusted with the use of a scantool like Espritmon or Freescan, and NEVER touched without following the correct procedure!

 

The never ever screw is the balance adjuster between the 2 sets of butterflies!  Never touch that!

The other screw is the minimum air rate bleed screw.  You CANNOT adjust this by ear. it will ONLY cause PROBLEMS if you do.

 

Read these threads

http://www.thelotusforums.com/forums/topic/57173-freescan-log-would-appeciate-some-input/?hl=%2Bminimum+%2Bair+%2Brate+%2Bbleed#entry454556

 

 

http://www.thelotusforums.com/forums/topic/46164-poor-idlestall-on-start-up/?hl=%20minimum%20%20air%20%20rate%20%20bleed

 

 

http://www.thelotusforums.com/forums/topic/43612-resetting-the-iac-on-freescan%E2%80%A6/?hl=%2Bminimum+%2Bair+%2Brate+%2Bbleed#entry363661

 

 

The green arrow is the minimum air rate bleed screw.  The red arrow is the throttle butterfly balance adjuster. NEVER touch that!

IMG_2727.JPG

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