Rough Idle/Poor fuel economy. Need help.

[primus]

Hello all glad to be part of the forums

To make a long story short, I recently bought a 2005 ford explorer XLT. I have always been a huge fan of these third generation explorers and I found a really nice opportunity to get a bigger car for my ever growing family and to get a truck I really like. Its been a hassle since I bought the truck since the previous owner really didn't do much to the truck. The past three weeks have been an ongoing mission to restore this truck to its working condition. Ever since I bought the truck, the engine motor has always had a little shake to it, and the idle was really rough.

Over the course of 3 weeks, I was able to do a tune-up, change the gas filter, transmission flush, differential flush, change the thermostat, switched to full synthetic oil etc etc. I was also able to seafoam my truck but the result of this seafoam were fouled spark plugs. Thankfully I did the seafoam before the tune-up. The seafoam results were not very satisfactory but my engine still has a rough idle and I am only get 10.7 mpg for both city and highway. According to my mechanic he said that I still have a rough idle due to a large amount of carbon build up inside the engine and I need to do a full engine cleaning in order to restore the idle and my fuel economy ($1,000.00 for labor and full cleaning .)

My question is that could carbon build up really cause my engine to have this much of a rough idle and bad fuel economy?

Thanks

 

[primus]

UPDATE

They installed a brand new throttle body which increased my fuel economy but my engine still has a rough idle and the engine still shakes. Any ideas?

 

[swshawaii]

Which engine? V6 or V8?

 

[primus]

I have a SOHC 4.0L V6.

 

[primus]

Why do I have the feeling that this is going to be solved by something as simple as a loose nut.

My mechanic recommended a full BG44K engine flush and clean out all the carbon inside the engine, another mechanic recommended me to change the O2 sensors, but if there was really a problem with the 02 sensors wouldn't the truck spit out a code of some sort?

I am going to try to clean a MAF sensor on the truck and see if that helps but other than that I am stumped.

 

[shadowless127]

Clean the IAC?

 

[MrBean]

i had the same issue, i was lucky to get 11mpg...it was too late to save my engine, ending up it was my #3 injector stuck open and it caused my engine to hydrolock...no codes

 

[tonydp]

I've had this problem for ever. Truck drives great but shakes at idle. The idle is steady, the truck just shakes. I just learned to deal with it. BTW I'm getting about 15mpg on my 02 4.0