Hard Idle when Cold
 

Hi Guys,

Monday arrive my 1985 Bronco with 302 Engine with Fuelinjetion in Germany.

I have a Problem when i start it cold in the Morning, it fires up without Problems, but than the rpm starts to go up and down, Engine shake badly and throtleresponce is also bad.

After around five Minutes it runs smoth at idle and has a good throttleresponce and no Problems, i am new in Fuelinjektion, so what did you think what can be the Problem?

Best regards

Torsten

Hi Torsten,
Awesome to hear of a Bronco in Germany!

This sounds like it could be a vacuum leak. This would be the same with both fuel injection and a carbureted engine.
If you have a vacuum leak, the ice cold air sucking in where it shouldn't would make the engine run really rough. Once it warms up, it has an easier time running with the cold air. Also, depending on where the leak is, metal expansion from heat can actually help seal the vacuum leak.

There may be other issues that could cause this, but this would be one to look into.

Hi,

thank you, yes Broncos are not that mutch on the Streets here ;-)

I will check for Vacuumleaks, i also think about the TPS Sensor and Idleairvalve, i will change them and see what happends. I know there is a Ford Manual for Emission and Injection but i cant find one to buy it and check all out step by step, so i am at try and Error.

regards

Torsten

Vacuum leaks, sticking IAC, bad TPS are all common causes of the rolling idle you describe. Add in worn throttlebody as well. It's a process of elimination.

Here is a good book;

This link may be of some help as well;
1986 EVTM - ???Gary's Garagemahal

Hi i get my Parts and start the troubleshoting,
- change the IAC = no effect
- change the TPS = no effect (what makes me wondering is that the engine still runs nearly the same as before, when the TPS is not coneceted to the wiring ???)

I let the Engine idle for ca. 5 minutes and that i see that the Exhaust in front of the Cat is start to glow red ? so i stop and dont let it warm up longer, nexst step will be to look for the Ignition Timing because the car gets a new Distributor in the USA before shipping! and than i will look at the MAP Sensor

I still search in the Dark and dont realy have an Idea

Best regards

Torsten​​​​​​​