I have a 383, headers, stall, XE 236/242 cam, etc in my car. I finally bought a new BBK 58mm throttle body for it. Well the car won't idle properly now. I am just wondering if I need to do some more tuning to make it run better now?

 

Exactly what it the problem? Wrong idle speed? Problem returing to correct idle speed? Rough idle? Hard to tell from "won't idle properly"

 

Soory about that. It idles much rougher than it did with the stocker, and stalls. Do you think I may have to alter the VE tables now that I have more airflow through the throttle body?

 

First you need to check the TPS voltage to see if it is correct at idle. On a lot of them you have to slot the holes in the TPS to adjust the TPS to the correct voltage. After that maybe adjust the throttle blade position screw to get your IAC counts right (maybe open up the blades more if it is stalling).

 

Why would there be more air flow through the throttle body at idle? The engine only uses the air it needs..... doesn't flow more just because you put a bigger TB in.

One of the common problems with large TB's on "cam" motors is "split BLM's"..... problems with the idle air circuit cause the left and right bank of the engine to run lean on one side and rich on the other, often maxing out the BLM's (long term fuel corrections) so they can not get the A/F ratio right at idle and low RPM.

Can you get a scanner on it, and look at:

-IAC counts
-TPS voltage
-left and right bank BLM's for Cell 16

 

Thanks for helping guys.

Fred, I'll try and get those numbers tonight.

 

Well I threw in some new plugs just to be sure.

Anyway both integrators are pegged at 193 and both fuel trims are at 160.

 

A wierd thing is happening.

The car will be idling very roughly, and seemingly very rich. Then all of a sudden the idle comes way up and it starts running much better. Almost seems like 2 more cylinders start firing.

So I log it idling. Again the integrators are pegged at 190 then suddenly when it starts running better they instantly go from 190 to 128 and the O2 voltages go rom 9.66 volts down to 6.56 volts. All in an instant. Then the car will slowly start to run poorly again, while the integrators slowly climb all the way back to 190 again, then the cycle will happen again.

The whole time this is happening the trims stay pegged at 160.

Fuel cell is 16.

I'm kinda stumped here................


O2 sensors both gone? I did get a right O2 sensor lean DTC once.

 

Any ideas?

 

I would guess a huge vacuum leak. Did you hook up the vacuum line on the bottom passenger side of the throttle body? The line from the pass valve cover to the throttle body? How about the gaskets for the top cover of the throttle body and the IAC gasket on the bottom? Elbow torn between the MAF and the throttle body?

 

Perhaps this link will help some..

http://www.hashmarks.com/techtips/throttle_body_mod.htm

 

Did you remember to swap the bottom plate from the stock TB to the new one?

Almost sounds like its dropping out of closed loop, if the INT's are going to 128. What is the coolant temp?

 

Yup, triple checked all that. All hoses are back where they are supposed to be, bottome plate installed correctly.

Coolant temp is about 185* (idleing for long time)

I could email you the log file I took last night.

 

Its pretty wierd how the left and right fuel trims stay pegged at 160, while the integrators are pegged at 193 then both suddenly drop to 128 at exactly the same time, then both slowly climb back to 193 again.

I am not sure if its dropping out of closed loop. I will have to watch that more closly.

 

And all this happened ONLY after you swapped out the TB?