okay.. 89 formula 305 tbi with headers. i have replaced everything except the distributor itself and i do mean everything.. the car is practically a 2014 when it comes to all sensors,connectors,seals,vacuums,electrical components etc. new tps,egr,aic,map,fuel pump,injectors,tbi rebuilt, etc.. runs great but when sitting at idle seams like a random miss or something. just idles rough. dont know if it could be the headers causing it or something im over looking. ive had this same prob since i bought the car and any advice would be appreciated. just in case it matters its a 5 speed. thanks

 

How many miles on this engine?

When you have a timing light on it, does the timing hold pretty steady, or jump around?

 

180k on the engine. ive never accually put a light on it. ive always timed it by ear and by how it cranks best and run best.. think it might be worn chain?

 

That says a lot.

 

At that mileage, a worn chain is possible. It's free to check, and eliminate as a possibility.

From my own experience with the L03 in my '91, and everything I've read here, these motors don't like a ton of advance. 4* to 6* BTDC seems to be the max. If fighting an issue, I'd go back to stock, which is straight up if I recall correctly, and tweak it from there. Don't forget to disconnect the EST bypass wire (I think that's what it's called) when checking the base timing.

 

thank you for the replies. ill check the timing asap a.d see whats going on.

 

Make sure the egr valve isn't stock open a little.
Check for slop in the distributor.