Erratic idle, what else i can check?

[wingrg]

Hi, 1998 Expi, 5.4 L, this it my second expi,
problem erratic idle on parking and while driving, no check engine light or codes.

work already done, new spark plugs, water pump, thermo.

What else i can check, in the morning everything works greats but about 5 min Driving start like missfire and when stop a little rought idle start, any sugestion or advice going to be apreciate.

 

[Eric]

My 05 does something similar and I can't find what is causing it. Mine runs smooth when the AC is on or when the engine is cold as the RPM's are up a little higher around 550 vs. about 500. In my case I'm starting to think its a lean condition purposely caused by the computer because as soon as I bring up the rpm's the idle smooths out, but I do get another shake at 1,200 ro 1,500 RPM when reving in park or neutral.

 

[tonydiv]

Do a search on the forum for "rough idle" There's a vacuum elbow that is problematic on the 5.4.

It could also be an IAC motor or coil packs, but look for vacuum issues first.

 

[wingrg]

TX for the advice apreciate this problem is giving me hard time and want to resolve by myself prior to start looking for a shop, I going to start to look if i can find that elbow.......

 

[tonydiv]

With all the vacuum lines running around that engine bay, it's so easy to disturb one when doing simple maintenance.

A can of starting fluid can help. Spray it around the vac lines, when the idle jumps up, you found your leak.

 

[wingrg]

Thanks for the advice i already buy the starting fluid can to make the test, i already check the elbow on the intake, but was prior replace with direct hose to the pvc, i can hear what i think is a little air leak going to test tomorrow morning and if no results was found going to verify coils, for my bad luck i already replace all the spark plugs this week and forget to check the coils arrrggggg.....OMG have to take out one by one again during this days to test the ohm reading on ea one, I have two xtra coils on my things one reads .5ohms the other one read is erratic that mean that one is bad right?, can anyone have an idea whats the reading in ohms for a good coil? thanks to all for the help.....

 

[burksfinancial]

I like that method. Another method is to get dish soap and water - put it in a spray bottle.....then spray the hoses. If it starts bubbling up - there's ur leak.

 

[wingrg]

Hi just a update on my case just verify cop only #7 was bad but problem continue, get to a racing shop of my friend and he scan the vehicle with a incredible scanner i dont have cel light on but scanner found open tps sensor, based on anyone experience is posible a bad tps cause rought idle autozone ask 45.00 for part any advice going to be apreciate. TX

 

[Eric]

One would think the throttle position sensor would not affect idle, but why would the scanner come back with a faulty code if it was good? $45 is not a huge chunk of change to spend by any means if it solves the problem. Can you buy the part, try it and if it does not change return it?

I have been through too many "diagnose by replacement" scenarios on vehicles so I'm cutting my losses on my Expedition and living with the rough idle. Still convinced it has to do with the coumputer controlled valve timing.

 

[wingrg]

Thanks its true, if i buy the tps i dont think i can return a electronic part but in my case when i buy this expi runs smooth later the cel light came on missfire on #7 change cop everything fine again later 3 weeks rought idle symptoms when stop and when driving and if i take a hill more rought also the cel lights blinks soon as i get home i try to pull any code with my little scanner no codes came up, i dont know what else to do i already chane spark plugs, 1 coil, going to verify for additional vacum leaks or bad cop, i dont know if i can spray the iac with carburator cleaner i just make once on my mustang and resolve the issue, well any results going to be post TX for the help