! Still having idling issues - Craig you there?

[Streetracer00]

After cruising, letting off of the throttle causes an almost immediate, single surge, then smoothing out of the idle, sometimes continuing to have a small slight surge. What is goin on? Craig Smith - do you have a number I can reach you at? I talked with Mike@FAST and I did not get very far. Also - I have a couple posts below that I wanted you to check out. Thanks!! You are the man!!

 

[55Belair]

Sounds like the throttle follower. the ramp may not be quick enough. causing the IAC to close too slowly after the fuel is stopped and causing it to lean out.

Also,Do you have any timing trim for Idle control in your setup?
If so, this may be the cause of the slight surging once it gets back to idle before it settles in. (mine is set at 0 timing trim)

 

[Streetracer00]

So the ramp should be sharp? Also I have no timing adjustment - it's set at 0 the whole time. Any other tips? Want to look at my program?

 

[bobc455]

No timing adjustment? Why not? (Do you still have the advance mechanisms in your distributor?)

Anyhow, not knowing anything about your program, I might start by looking at the A/F setting at the appropriate point on the chart, and making sure your VE numbers are realistic. VE numbers for decelleration are very hard to set accurately because the engine situation is very dynamic and you have very low airflow (meaning you have a lot of lag time to your sensor, especially if it is further downstream in the exhaust).

Personally, I don't really use the throttle follower- my thinking is that since when you let off your TPS goes to zero, your throttle follower goes to wherever your idle setpoint is. I've played around with it and never seen a difference, so I just zeroed it out. (Your mileage may vary)

I agree on the zero timing trim method.

Streetracer00, I guess I would go after the VE tables (assuming your A/F table is realistic)- go on the highway and record a decel from 70 to 45 or so (depending on your local speed laws) and see if there is a lot of O2 correction (keeping in mind the delayed reaction because of the very low airflow).

Maybe you could clarify a bit what you mean by a surge- does the engine go down to normal, then up, then down? Or does the engine speed drop so low that the engine starts to stall, then recovers?

-Bob Cunningham
bobc@gnttype.org

 

[Streetracer00]

bobc455

A few clarifications.. sorry, I do have timing adjustment, I meant I was not using any "timing trim" As far as the surge, it surges like this. I'm cruising at say 55 MPH, then I come to a stop light. I push the clutch in, move the shifter to neutral, and the motor drops down to an extremely low RPM (almost stall), surges back up high (1600-2000 RPMs), and then tries to settle down.. sometimes it never fully settles down, but does a very small up/down surge.

Recording the decel - should I just take the car up to 70, activate the datalog, and put the car in neutral?

Obviously I'm a little new to this Thanks for all the tips so far!!

 

[Craig Smith]

I'll bet your throttle blades aren't open far enough, and the IAC is the only thing keeping the engine running. This is a common cause of this problem.

Look in the throttle follower screen and adjust the throttle blades so the the IAC target is at about 25 or so. Make sure the throttle follower graph is set so that at idle the IAC target is just above the line in the graph.