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Ask Derek Werner Your Own Question
Derek Werner
Derek Werner, ASE Certified Technician
Category: Ford
Satisfied Customers: 135
Experience:  ASE Master Technician, L1 Advanced level specialist
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1999 f250 super duty 4x4 6.8 auto truck has 187k - the truck

Customer Question

1999 f250 super duty 4x4 6.8 auto truck has 187k - the truck is having a number of issues. first off the idle is extremely rough almost like a lope and feels like its gonna die in gear when its at a stop. The next issue is when coming to a stop the rpms wont drop coming to a stop I literally have to hold the brakes till they eventually return to idle. I am getting po135 and po155 codes on O2's that are less than 6 mos. old. and finally my brand new radio intermittently turns off or loses its memory and I had the install double checked - I've checked for vacuum leaks, replaced the IAC, plus this short list 1. replaced central junction box for no start 2. replaced all plugs and coils, coolant system tested and serviced, had it checked for a faulty ground, had the fuel system serviced, compression test, - all done by a local Ford dealership. the truck starts fine, no smoke, no burning oil, no leaks. just 3k in a truck that still runs rough any help would be appreciated
Submitted: 6 months ago.
Category: Ford
Expert:  Derek Werner replied 6 months ago.
sorry i responded to the wrong question, i will opt out.
Customer: replied 6 months ago.
fuel pump pressure was tested during no start issue that was resolved - Dupratt ford it was good. I will try cleaning the MAF
Expert:  Derek Werner replied 6 months ago.
Sorry i was having a computer problem and sent that message to you by accident. I can still help you if you like. Cleaning the MAF is a good place to start. Are you having a rough idle also?
Expert:  Derek Werner replied 6 months ago.
nevermind you already said that, i am looking up some information on your problem now
Expert:  Derek Werner replied 6 months ago.
Can you check fuse number 7 in the underhood fuse box. If this fuse is open it can cause the problem you are describing. Thanks Derek
Customer: replied 6 months ago.
Fuse #7 is good
Expert:  Derek Werner replied 6 months ago.
P0135 and P0155 are oxygen sensor fault codes. The most likely cause for this is a vacuum leak. I would highly recommend re testing for a vacuum leak. From the symptom you described, a high idle and loping idle. This sounds exactly like a problem i had with a ford not long ago, and it was all caused by a vacuum leak. To check for a vacuum leak you can spray the intake area with brake clean with the engine running. If the RPMS smooth out or go up then you have found your leak. Just be careful doing this brake clean is flammable don't spray to much brake clean at a time. The most common causes for a vacuum leak is the pcv elbow behind the throttle body. Double check the pcv tubes that route from the valve covers to the intake.
Expert:  Derek Werner replied 6 months ago.
The best and most safe way to test for a vacuum leak is using a EVAP smoke machine. The throttle body is blocked off and smoke is induced into the intake system, If there is a leak you will find smoke from the source. Most shops have this tool to check for leaks, some people dont always use the smoke machine to test for this though as it takes more time.