I have quite a pickle on my hands. I have a 1993 F-150 5.0 2WD that I have been working on for quite some time and am still having trouble out of. The previous owner had rigged and botched multiple things under the hood that I have spent countless hours toiling over, repairing and replacing parts back to stock. Here's the DL. The truck barely ran at first. The EGR and ignition systems were totally jacked. I've replaced the EGR valve, EGR tube from the valve to the manifold, the EGR solenoid. I've replaced The ignition coil, ignition control module, The distributor, cap, rotor, plugs, plug wires, the pcv valve. I had to replace the throttle body because somebody had bypassed and plugged the coolant line that ran to it. I also replaced the IAC on the throttle.

Here is my current issue. When I start it up, it has a rough idle for a moment and then surges up to around 1200ish rpm. When i rev it up, she spits out whitish/grey smoke that reeks of gas. All of the emissions plumbing is correct and properly attached so I shouldn't have vacuum leaks, yet here I am with high idle. I ran it through emissions and my hydrocarbons are outstanding, as well. Some people say the TPS is possible bad, some say intake manifold leak, some say blown head gasket. I would love any suggestions. I'm not giving up on this old bird just yet!

 

i guess i will have to do until one of the old pros steps in ...

forget about people who say "it's the alternator", or "the pcv", unless you have some real solid clues to point you to a specific area, your first steps should be 1) check compression 2) check codes. armed with that info the wizards here can save you a lot of time and money.

 

Well I'm no pro either but my intake plenum had a leak in it and it did pretty much the same thing. Have it running and spray some carb cleaner around where it meets the intake manifold.Note any change in the idle.

 

It doesn't sound major. You've replaced everything that should make it run perfect. But the high idle, and white smoke sounds like it's just been sitting or doesn't get driven a lot. When mine sits it does the EXACT same thing..

 

I drove it again today. Still smoking, and the idle is erratic when you take off. I had to pop the clutch a little to keep it moving :/. When I got it home i ran a KOEO test. Its giving me codes 34 and 81. Everything in the EGR is replaced and tested so I'm not as worried about 34. But 81 is new to me. I'll try the starting fluid test, but just to make sure, I found a stethoscope today; that might help find a hiss if its a manifold leak . Beyond that I'll have a compression test run.

 

How's your fuel pressure? My truck (dual tanks) has a failing Fuel Delivery Module in the rear tank... weak pump and leaking check valve. If I try to start it on that tank, especially for her first startup of the day and without priming the fuel system first, she struggles to make it up to idle, then revs up to high idle just like yours does. Lights off right quick if I'm using the front tank.

The white smoke could be an injector or two leaking while the engine is off. Which might also explain why she struggles to start/idle... if that was the case then the fuel system would lose it's prime and the truck would be hard to start, and when it did it'd be burning off that extra fuel.

Not saying this is the case for sure, just something to consider. Can't hurt to check.

 

My car had very similar symptoms when the dealership replaced the PCV valve with the wrong part. It idled very high as if the choke was stuck on. Then when I gave it some throttle it seemed like the rpms had been capped. When I really got on it, it was as if a white smoke grenade popped out of my exhaust pipe (thankfully this happened in the middle of a busy intersection). Check to make sure you've replaced all of your emissions equipment correctly and with the correct parts for your application. Good luck!

 

toby tough is probably right, I also had a truck that had idle flux I thought it was the EGR, then the IAC and it turned out the intake manifold gasket was bad. Replaced those and never had another problem. Although I did try to spray them to see if the idle would change and it did not, they were blown on the inward side not the outward side.