Running rough at 45 mph and surging at idle

[draco880]

Hi there, I have a 1994 XLT, V6 with 160K on it which I purchased used a few months back. The oil and oil filter was changed recently, as was the air filter. Recently I was driving back from the airport and noticed that the car would begin to shake at about 45 mph, although it was fine at 55. On the way back it developed a noise like air or fluid being cycled, kind of a whooshing noise that did not change at different RPMs. When I had to stop at a light, I found it was also surging at idle. None of the gauges changed during this, other than the tach during the surging. When I got home I let it idle for a while and it sounded pretty sure it was going to die.
I'm going to pull the plugs, but I was hoping folks could advise me what I should check first after that. I did a search for surging and also read through posts I could find that seemed relevant, but nothing was really identical with this problem. Anyway, I'm grateful for any assistance.

 

[ma96782]

IMHO.....for those that have just purchased a USED vehicle from someone (questionable history) and have noticed some issues...............

I suggest a complete tune up..............include the: air filter, motor flush and re-fill w/oil and new filter, fuel filter, pcv, cooling system flush and re-fill w/ new coolant, plugs and wires, run some sea foam, and don't forget the fuel system cleaner added to the fuel.

Clean the MAF and IAC.

IF you feel energetic........do the transfer case, frt diff. and rear diff........expand that to a check of the breaks, trans and motor mounts.........shocks and RAB. Anything else....feel free to, "just do it."

Check for codes.

Aloha,Mark

 

[taxx]

Clean the MAF and IAC.

That is the big one. Both can cause a crappy idle. IAC may even be going bad, easy enough to clean it and check it out though.

The 45mph issue? Is it running rough? or is the truck vibrating? Could be out of balance tires if the latter. If its rough, whats the RPM difference between the 45 and 55? could be associated with the MAF or IAC or plugs or air filter or plug wires....

I would stay away from the sea foam though

 

[Maniak]

Since you mentioned surging idle.. I'd also say check/replace the TPS. The TPS voltage should move smoothly as you open the throttle.. sudden jumps is bad.

Oh yea.. a vacuum can do it too.. The computer will attempt to keep the vehicle from stalling which would make it seem like it is surging

~Mark

 

[Wrench]

taxx - any reason you appose the use of sea foam? I've often wondered what damage it might do to the o2 sensors.

 

[taxx]

taxx - any reason you appose the use of sea foam? I've often wondered what damage it might do to the o2 sensors.

Just never had any luck with any kind of magic fluids. I know some swear by it, but I get on too many forums and see the miussuse of it causing major problems. Why risk it?

Besides it sounds like he has other issues. I doubt its a clogged injector and gummed up piston.

I think the suggestions above are right on the right track.

 

[draco880]

As it turns out, the fix was pretty simple. One of the tubes off the back of the vacuum tree had just fallen off. Thanks very much for the suggestions, though. Once I get some free time I'll get it properly cleaned up and see if I can head off any more major problems.

 

[draco880]

Oh, and the IAC was also pretty filthy, although clearly the vacuum problem was the big one.