I have a 2000 F-150 with a 4.2L. For a while now the truck has a hard time running. Whenever I start it up it idles really rough. The RPMs will drop down to maybe 200-400 then jump up to 2000 and come back down to 1000 then drops again and dies. When I am lucky enough to get it moving after waiting 15 to 20 mins for it to calm down it has no power. It drives really rough. It always sounds like its going to die. It feels like it is misfiring when I go up slight inclines or even to slightly accelerate. It also pops like a misire when under a regular load. It can barely reach 60 mph. It has also progressively gotten worse over the past few months. I had a CEL about 1-2 months ago and it went away, but it was cylinder 2 misfire and catalyst efficency below threshold. The shop guy told me that is was a clogged converter causing the misfire and everything else. I didn't get the converters replaced yet. Tight on money. Plus I didn't believe him because I have unbolted the exhaust from the manifold and it changed nothing. But for the past 2-3 weeks there has not been any codes. I have read many other forums of guys who have had very similar problems and I replaced everything they said caused their problem but nothing has fixed mine yet. Here are the things I have already replaced: EGR valve, DPFE sensor, Mass air flow sensor, spark plugs, plug wires, oxygen sensors, fuel pump, fuel filter, and used seafoam to clean injectors. I need help in the worse way.

Thanks in advance for all your help!

 

my old 3.8l stang used to do that in the cold and never discovered the main cause of that issue but changing the fuel filter did wonders since it was original.

 

Check and or clean the Idle Air Control Valve...the IAC. If dirty or defective it will cause stalling and or rough idle........

 

Didn't catch how many miles on the engine, have an 02 4.2. 178K. Haven't had much trouble with mine at all to offer up any tune stuff. Might go old school and do a compression check, if engine will allow, at idle, pull one plug wire at a time to hopefully locate which cylinder is the miss. Believe you said no codes lately, what were they before? Am not sure how to verify if PCM will throw codes, other than disconnecting a sensor. Don 't hesitate to post a new thread in either the 97 - 03 section or in Engine talk. Might catch the eye of just the right guy. An awful lot of newer guys with post counts alot lower than me who know a whole bunch more. Good luck and will be checking your results.

 

I would be very interested if you learn anything that might help. My 2001 5.4 4x4 is doing exactly the same thing except the idle problem and for now mine is intermittant but seems to be getting worse as time goes by. I used to notice it only when the engine was hot but it seems there is no certian condition when it acts up.

 

Idle control valve or sensor, egr valve or sensor, and a good cleaning of the inlets on the t-body for the egr, best to remove from engine it will clean up better this solved my problems on my 5.4 same symptoms you are having! also check hoses for vacume leaks

 

Thanks, I'll give it a shot.

 

I have about 150K on my truck. Everyday I look at it to see if I can see anything different. I haven't checked the idle control valve or sensor. Would that affect how it would run at hiway speeds? Is there any way to check or test the sensor or valve to see if that is causing the problem?

 

My limited knowledge of the IAC is that it controls idle speeds through the PCM (computor). Don't believe it has any function once the throttle is opened by the accelerator cable. This engine is really messed up. Need a compression test to be sure the basic engine is OK. If a tester is not available, pull all plug wires off and crank engine over with starter. If a cylinder is bad there will be a different sound of the starter motor when it hits the weak cylinder. Are you sure the CEL bulb is working? Turn on the key, does it come on then? If its an electronic issue, it should be throwing codes.

 

Yea, the CEL comes on with the ignition on. I haven't checked the compression yet. I should do that. It might be a little while before I can look at it again, with the holidays coming up need money for gifts. Thanks for all the inputs. I will keep you guys updated, of course, if and when I find something. Please keep the ideas and suggestions coming.