I bought this 1989 formula 350, with 68K miles on it, runs great, but surges at idle, but goes away once its warmed up. It has new plug wires, new bosch platinum plugs, I run 17* base timing, TPS voltage is at .5V and has a K&N air filter, and a magna flow exhaust, and the dual cat option, along with a limited slip 9-bolt rear end. I also replaced the plenum with one I ported slightly, and de screened the MAF and am going to put an adjustable pressure regulator in it soon.

So I'vce checked out all the vacuum lines, and Can't seem to find any leaks. The Maf is good, and I replaced the relays, and all seems to be fine, but I can't seem to figure this out, and I'm almost a technician.

I also tested the IAC and swapped it for the one I had in my iroc, and no difference, I'm kind of stumped.

Do any of you have any reccomendations for other things to try?

I mean the spark seems to be fine, and the module is working alright because when you rev up the motor, it runs like a top! But still surging at idle, so I'm just stumped, and thought I'd see if the fellow thirdgener's could help a brother out! Keith

This new car is at www.cardomain.com/id/cronsformula its the red one

 

Aside from tearing your throttle body apart and giving it a good cleaning.......
I had a similar problem. There were no apparent mechanical issues.
Turns out I had to remove a lot of fuel and spark advance at idle to stop the surge.

17deg base timing? You're not talking mechanical timing which should be set at 6 are you?

 

If you or someone else set the timing without disconnecting the distributor wire, that'll cause a surge,,, especially if the base timing is really at 17-degrees. Disconnect the wire for the dizzy, set the base timing to 10-degrees, then reset your min air speed idle (correlation between the timing, IAC solenoid, idle screw, and TPS) and see what that does for you.

 

I ran the timing the same in both of my f-bodies, my 87 iroc-z and ran thirteens with a slipping trans and in my formula it ran great, and no surging, but I run 14* timing with my HSR and 37.5 psi right now, because the computer isn't tuned for 24# injectors yet, so it runs a little less gas with 4 holes shooting fuel out, so they have a good spray pattern.

The other two tone formula, my moms new toy; we changed the plugs, the plug wires are newer, I changed the O2 sensor, because it was coated with a powdery white residue from contamination, from using silicone or something of that nature, so it needed to be changed. I changed the plenum to a ported one behind the TB, and am running stock 42psi for now, but will change later and add Edelbrock shorties for power and ground clearance, but may run a true dual exhaust to the back, but has a magnaaflow for now.

But I also tightened the throttle body, and there seem to be no leaks, but I will change the lower TPI Gaskets and the o-rings on the injectors, because I belive they're stock, and may be leaking some air, confusing the MAF sensor. All the other vacuum lines seem like they aren't leaking, because I used the propane trick, but no dice.

What else do you fellow third genners think? I tested the IAC and its working fine, but even on a cold start up, it may start and die the first time, but its intermitent, so I'm going to ALL Data it and see whats up. Let me know what you guys think, thanks. Cronsformula