Ford explorer 98 cold start rough idle
 

Alright so I have a 4.0 sohc it runs great besides when I first start it it won't idle unless I run the engine at high rpms. I've checked for vacuum leaks replaced spark plugs and my coil pack along with my mass airflow sensor and my dpfe/egr sensor all have helped with performance. If I do drive it at high rpm for about 10 min it will idle but I would like to start it and let it warm up since it's winter and I'm getting tired of throwing money to just have little improvements with its overall driving. I do the repairs myself and would like to find a solution please help!!

I am curious if it has anything to do with the cat but I don't want to replace it if it doesn't help

Welcome to FTE.

Have you tried a code reader to see if there are any stored codes?

These commonly have intake o-ring and intake crack issues. You have checked for vacuum leaks, but did you check the manifold and manifold to head connections, not just vacuum lines?

Thank you. I have not checked the intake manifold O-rings I could check it out. But would that have anything to do with the fact that it's only when it's cold or could the O-rings expand once they heat up?

If it reliably runs better once it's warmed up, I would suspect a temperature sensor. Have you tried pulling codes yet?

I did pull codes. I took it to auto zone and the code reader recommended a mass airflow sensor and that I was having miss fires in 1,5, and 6 with a few other codes like not getting enough fuel. I haven't been too worried about my mass airflow sensor since I replaced it less then two years ago. I'lol prolly pull codes again and see if anything comes up different and post the results. The codes are why I put a new coil packs in.

Misfire in a few cylinders points to plug, coil or vacuum leak at that cylinder. Since you did the plugs, o-rings become a suspect.

These usually give a lean code or an oxygen sensor code. The sensor isn't bad, it's just giving a code.

And to answer your earlier question, yes, once warm everything expands a bit.

As for the cat, which you mentioned earlier, if it were partially plugged you would still have a smooth idle but you would lack for power at higher revs and under load.

Ok that makes sense I pulled codes again and it did recommend intake gasket I was recommended to use a copper spray on the gasket and everything will be good what do you think?

Copper spray on the gasket....I don't think so. These are plastic on plastic with o-rings, not a one piece gasket like older/other engines with metal intakes. There are two parts to this video, and it is a bit tedious. BUT it gives a clear view of the process and the intake sealing surfaces.



Once you get on there, other Exploder/Ranger 4.0 SOHC videos show up.

Thank you I decided against the copper and I did buy all the gaskets