Hey all.. my 94 AWD EB is running rough. New tune up, and the shop says they think it runs ok. It's not terrible.. kind of a stumbling when stopped or idling. When accelerating, it seems to hesitate and have no power until it gets higher in the powerband. I unplugged the MAF sensor the other day and started it.. it did affect the idle.. but not much. When I get home from my 5 mile drive home from work and turn off the car, it smells.. basically.. hot. Temp is ok on the gauge, and the shop says the van is mechanically good.. but any ideas? I was going to replace the MAF, but don't want to throw money at parts for no reason. The engine has no codes. Maybe a TPS? The IAC looks original as well.. and hard to reach lol.. any ideas? I'm afraid to take it back to the shop when they say it runs fine.. but you can hear the stumble of the idle in the power steering pump.. and I get about 14 MPG in the city..

 

I would start with the simple things first.

The symptoms you describe seem similar to a vacuum leak, so try to find that first, specifically around the vacuum tree at the rear of the intake manifold. You will have to remove the dog house cover, and look toward the driver's side. My engine sometimes backfires if I don't start it "right", and it blows off caps on the tree. The cap would disappear, leaving a huge air leak into the engine. I've since replaced a couple of the caps with a short length of hose looped between two of the nipples. If the engine backfires again, it will blow one end of the hose off, but it will remain attached on the other end, and I can re-connect the loose end.

The MAF sensor may not come into play when the engine is cold. So even if it was broken, your engine would start and run from cold, seemingly normally. Then when the engine warms up and starts to run in closed loop, a broken MAF sensor will start making the engine run badly; usually very badly.

You can check the IAC by unplugging it while the engine is idling. Again, it might be more effective to do this when the engine is cold, and is relying on the valve to maintain idle. Pulling it should cause the idle speed to drop, maybe even stall the engine.

 

I agree with xlt4wd90 regarding the vacuum leak. Also look at the small vacuum lines in the engine compartment on the passenger side. These are plastic and become brittle with age. Any service done in the engine compartment can fracture these small lines without being noticed. I too, have had the backfire start issue blow off the two capped ports on the vacuum tree. I replaced the caps but put spring clamps on them with no further problems.

Also, you can "test" the IAC by warming the engine and then turning on the AC. If functioning properly, the IAC will kick up the idle slightly to compensate for the load placed on the engine by the AC compressor. Of course, this will be hard to detect if there is a vacuum leak present.

A cheap vacuum tester/gauge will help to pinpoint vacuum leaks being present.

 

another likely culprit and common vac. line failure in these is the gas fumes purge system lines and fittings under the air cleaner housing and the line running over to the throttle body.
gas fumes passing thru these eat them up every few years.
use a high grade of gas proof hose on these, spend the money and save redoing the job.
doesn't always throw a code.

had to replace the purge system 2 times on mine, the last time with the best quality expensive hose I could find. hell to work on in there. the line across the top of the engine to the throttle body was an intermittent leak horror, just threw it away and replaced.

cleaning the throttle body throat and back edge of the TB plate helps immensely on these. dust and grime gums up the fine idle gap and plate movement gap varies. every 20k miles. city street driving is dirty. TB or carb cleaner and a clean shop rag, NOT while running.

got to do an engine douche on these. the 4L carbons up severely especially in cold short trip city driving.
see:
https://www.ford-trucks.com/forums/1...arbon-tsb.html

I like straight acetone, cheap paint store variety, 1 qt with a cup of kerosene, some like Seafoam, too expensive for my wallet.
sucked slowing thru a 1/8 plastic tube into the throttle body plate gap at 2000 rpm. shut off engine. let soak for an hour and out the the freeway to blast it out.


rough running while cruising and part throttle acellerating with decrease in MPG can be a sign of O2 sensor failure.
they only last approx 80k miles on these, can fail sooner, become coated with deposits or active component drops out of spec.
common service item like spark plugs. 80k is a good time to replace both.

what brand of plugs and plug wires used?
The Motorcraft or Autolite double plats or Iridium plugs are the only ones that hold up and have the correct heat range for the unique waste spark system.

Motorcraft ign. wires only. the other brands have wrong length which leads to wires laying on metal with heat damage, loose ends, poor insulation heat break down. ad naseum.

14 mpg is about right in slow city stop and go driving for these. RWD and shorties get somewhat better

Is it using any coolant? level dropping?

also check the rubber vac. line to the fuel pressure regulator and to the auto tranny vac. modulator on the passenger side up behind the muffler.

both of these break down often and leak or the vac. modulator diaphram breaks down and the engine sucks back ATF into the engine intake manifold. both cause idle and engine run issues

finally solved my long term rough running problems early this spring after more than a year. mine ended up being plugged orifice in the exhaust pipe section of the EGR system.
Runs the best it's ran in years. goes like hell and roars on the freeway on ramps now. MPG freeway back up to 20+ mph
gonna keep the old girl for awhile, most dependable rig I've ever owned. Just can't work on it any longer.

everything on these is hard to reach, access. even the gas cap if you have big hands.