More Idle Questions

Tim_D

Active Member
In a previous thread we discussed some issues I was having with getting my engine running correctly, after initial installation into a new chassis. Very helpful people helped me to establish I had fuel injector (minor) and MAF (major) issues. The car runs pretty darned well currently.

However, I do have a question with regards to idle quality. When first started (cold), idle is very smooth. Once it gets to operating temperature, it "hunts" between 650-750 rpm.

A little background on the engine:

Essentially stock with a few exceptions:
1. LT1 3" MAF sensor and translator
2. Accel 30lb injectors (42s and a chip to be installed soon)
3. K&N cone filter
4. A bunch of stock-level replacement parts, including plug wires, crank sensor, coolant temp sensor, air temp sensor, knock sensor, oil pressure sensor, every vacuum line, all gaskets, timing chain

Things I've verified include:
a) Vacuum reads 18-20in consistently (I have an aftermarket vacuum/boost gauge from Auto Meter, run from the MAP sensor port)
b) No SES codes

I understand that the stock chip uses open loop idle at cold, and closed loop at warm. Also that aftermarket chips generally use open loop idle always. Is this because of stock idle quality issues?

Thanks in advance -
 
[QUOTE="
I understand that the stock chip uses open loop idle at cold, and closed loop at warm. Also that aftermarket chips generally use open loop idle always. Is this because of stock idle quality issues?
Thanks in advance -[/QUOTE]
That's the main reason. TT chips are usually open loop idle unless you request closed loop idle.
 
Yes, most aftermarket chips utilize open loop at idle, as mikestertwo has said, TT chips utilize open loop idle, but can be changed to run closed loop in the parameters if you so desire, 100 rpm fluctuation at idle isn't too bad, that's about where mine runs, between 75 and 100 rpm "hunt" at idle.
 
You already found your problem. The stock chip belongs in a museum not in an ECM.

^^ X2
Cold start ups with my stock chip and Kenne - bell hot flash chips were time consuming as they would go to high idle right off the bat, stay there for a couple minutes then would go to low idle (uh oh, too lean) stumble, back to high idle for a couple more minutes then back to low idle (uh oh, still too lean) back to high idle and so on.

It wasn't until I got the ATR Pitbull Street Chip in '89 that the cold start up was the way it should have been and drivability was amazing, oh my, it was glorious. Lol, so much better.

I think you will be surprised and very very happy with the drivability of a modern chip.

I wouldn't worry about it until you get the new chip and injectors in it and see where your at.
 
I guess I have not noticed idle and drive-ability to be that bad... But then again, every hot rod I've ever owned has been a 60's-era car with a carbureted V8. Those things aren't too well known for crisp idle and throttle response. And the car I'm driving is still a 60's era hot rod, albeit with a (more) modern FI powertrain.

However, when you take the perspective of drive-ability as compared to a modern FI hot rod, it's then that I see some shortcomings. So a modern chip tuned to my combination should really help out with that regard. Looking forward to it!
 
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