Well, I have posted many times before on my rough idle problems. 91 F250 w/351. Symptoms: Rough idle, also not smooth reving in park from idle to around 2K. Seems worse when cold. Does not however seem to affect drivability, just annoying when idling.
I have done the tuneup items myself which include, all filters, cap, rotor, wires, plugs, ECT, cleaned IAC, cleaned intake and TB.

Taken it to two mechanics including a friend who works at a Ford dealership.

After replacing thermostat, coil, 02 sensor. Both of them said everything has checked out normal, even did a cylinder balance test and everything is good. Last guy tried an injector cleaner machine to see if that would help. He also is at a lost on what to do. He said that after talking to another older mechanic at Ford, that guys thought he remembers a common problem with this truck which was attributed to a firing order which they changed later to correct.

Any thoughts?

 

Hmmm. I read this before and I still have no clue. I would recommend finding a buddy with the same truck and computer, and swap computers and see what happens. I mean all you can do is try. Thats the only thing I can come up with.

 

"firing order which they changed later to correct"

They changed the firing order on the 5.0 (302) not the 351W.

 

From what the mechanic said it isn't a ignition miss so I am thinking it is some kind of mechanical valve or component that doesn't throw a code or a hard to find vacuum leak. If anyone has another idea please keep em coming.

 

Vaccum leaks aren't hard to find. Attach a vaccum gauge and watch the needles at idle. If you have low vaccum, or wavy vaccum (or both!) then you have a vaccum related issue which could be many many things of course. A windex bottle full of soapy water liberally sprayed where leaks can occur are good ways to find them. If the soapy water hits the engine, hose, manifold, brake booster and so forth, and quickly disappears (i.e. gets sucked in) there's one leak. If you find one, don't stop there. You might have two, or three, or six.

Let me ask you this.... does it idle the same with, or without the SPOUT connector in?

If you have hydraulic lifters it's possible that one's floating or not pumping up all the way, however when the mechanics did the compression test I would have expected that to show up.

It runs okay if you rev it? Purrs like a kitten? Or is it rough to some particular RPM? Knowing that might give me some ideas.

Could even be timing chain slop, though I doubt it thinking about it.

 

Pull the distributor and see if there is excessive slop in it. This may cause the problem

 

Also, the throttle body may be leaking around the shafts. Do they have a lot of play?

 

Frederic,
The Ford mechanic friend said that he used a whole can of WD-40 trying to find a leak and couldn't find anything. I also tried a propane torch and had no luck. I am starting to think its not a vacuum leak.

Regarding the spout connector, what exactly is that and where is it located so I can try that next?

The rough idle occurs whether its hot or cold. It might be my imagination but it seems to occur in a pattern, like it occurs every 2 seconds or so.

If I rev it in park, it doesn't rev very smooth like it should. It does this from idle to about 2K and then it is either is too hard to detect or it goes way, I am not sure.

Drivability wise, since the truck is new to me, I am not sure if it is driving correctly, it seems to drive alright and I am not sure if I detect the rough running while driving.

Any thoughts?

toyscout2,
how exactly would I check the throttle body for play?

 

has anyone put a code scanner on it?? it is possible the cel is actually on, but the bulb is bad. that sounds alot like an egr problem.

 

Yes, when I first got the truck I pulled codes and got a code 327 "EVP or DPFE circuit below minimum voltage". My CEL is burnt out so I probably have something causing the light to go on. I was told that this code is pretty common and that it is probably due to something else so I didn't pursue it further. I did take EGR apart and clean the valve after I got that code but haven't checked codes since. I just assume the two mechanics would have checked codes also when they were looking for the problem. Any thoughts?

 

The spout connector is near the TFI module, which is a gray or black "thingy" mounted on a heat sink near the back of the driver side fender *OR* it's mounted directly on the distributor. It's a little connector with a "plug" in it, that essentially shorts the two wires together. When you remove the plug, the computer can no longer adjust the timing, and your static timing, based on distributor position, determines your only timing. The timing at idle will be fixed, and should be at 10 degrees. If the dizzy is at 10 degrees, and the idle suddenly gets better, it's either the computer or the TFI module. The TFI modules do go bad because they dislike heat, and of course it's hot under the engine compartment, especially if it's mounted on the dizzy. Try that first and see how you make out. Sometimes the issue is the connector on the TFI module itself. Take it off, plug it in, take it off, plug it in, so you can get a good connection. Poor connection can cause an erratic idle.

Others have suggested dizzy slop, which is very possible. If it's not vaccum related, it's probably timing related. I'd yank the spout connector out first because it's easy to do, and doesn't cost you any money and certainly very little time. If that doesn't do it, then you can check the dizzy for slop. I assume the bolt/fork that holds the dizzy in place is tight, correct? It doesn't need to be torqued to 80 ft-lbs or anything but it should be tight enough to hold the dizzy in place. A wiggling dizzy isn't good for rock solid timing.

This leads me away from vaccum issues and more towards timing issues.

If the engine has good, balanced compression and everything is working correctly, it should have a smooth idle, no hesistation, and give reasonable power throughout the RPM band. I have over 350K on my crewcab and the idle still is stable as all hell. Of course I've had to replace quite a few parts along the way as things... well... break.

Let me know how you make out.

 

How to fix code 327:

From the Ford service manual:

1. Run engine until normal operating temperature is reached.

2. With engine running at idle, disconnect EGR vacuum supply at the EGR valve and check for a vacuum signal.

NOTE:
The EVR solenoid has a constant internal leak. You may notice a small vacuum signal. This signal should be less than 3.4 kPa (1.0 in-Hg) at idle.

3. Is EGR vacuum signal less than 3.4 kPa (1.0 in-Hg) at idle?

If not, then INSPECT EVR solenoid for leakage.

And yes, it is a duty cycle component. From the manual:

The EGR Electronic Vacuum Regulator (EVR) solenoid is an electromagnetic device which controls vacuum output to the EGR valve. An electric current in the coil induces a magnetic field in the armature which pulls on a disk closing the vent to atmosphere. The Powertrain Control Module (PCM) outputs a duty cycle to the EVR which regulates the vacuum level to the EGR valve. As the duty cycle is increased, so is the vacuum signal to the EGR valve. The vacuum source is manifold vacuum.



And here is what Haynes says to do:

Electronic fuel injected systems operation and checks

EVR Solenoid Valve Operational Checks
47 Vehicles with EFI use only one solenoid valve to control vacuum to the EGR valve, the Exhaust Valve Regulator (EVR) (see illustration). In operation, the EVR is supplied a continuous source of manifold vacuum at its inlet port. When directed (energized) by the PCM, it will open from its normal closed position and allow vacuum to the EGR valve. When the EGR valve opens to the proper position (EVP sensor indicates position to PCM), the PCM will turn the EVR off and the solenoid closes. Vacuum between the EGR valve and the EVR solenoid valve now vents through the EVR valve, allowing the EGR valve to move to a more closed position. To maintain the EGR in desired (Hold) position, the PCM must again direct (energize) the EVR to open, and the cycle continuously repeats. To change EGR valve position, the PCM simply holds the EVR open longer (opens EGR further) or closed longer (closes EGR valve further). This duty cycle occurs continuously, maintaining the EGR valve at the desired position. The EVR solenoid is provided continuous voltage in RUN position, the PCM completes the circuit on ground side by alternately grounding and opening circuit. Caution: A small leakage during valve closed tests is considered acceptable.

48 The conditions for testing are as follows:
Engine not running, key off, EVR electric connector disconnected.

49 Remove the vacuum supply line from the EVR solenoid. Install a vacuum gauge to the EVR outlet port and using a hand-held vacuum pump, apply vacuum to the manifold vacuum supply inlet port. Vacuum should hold and no vacuum should be indicated at the gauge. If not, replace valve.

50 Install ground jumper to one EVR solenoid terminal and a 12-volt source jumper to the other to open valve. Release trapped vacuum if required and repeat the vacuum pump test. Vacuum should now be indicated on the gauge and vacuum should hold. If not, replace the valve set. Caution: Do not leave the hot (battery) jumper installed any longer than necessary.

51 Remove the jumpers to close the valve and connect the vacuum pump to the EVR outlet port. Apply vacuum to the port to test venting. Vacuum should bleed. If not, replace the valve.

52 Measure the resistance of the solenoid valve at its electrical terminals. Resistance should be between 20 to 70 ohms except for the 7.5L engine, which should be between 100 to 135 ohms. If not, replace the valve.

53 If all checks pass, the EVR solenoid valve is operational - proceed to the circuit checks.

EVR circuit checks

65 Disconnect the EVR electrical connector.

66 With ignition switch in RUN position, check for voltage at B+ (VPWR) terminal on the EVR electrical connector (see illustration). Greater than 10.5 volts should be indicated. If not, proceed to Chapter 4 Section 15 and perform the EEC power relay checks to obtain voltage.

67 Disconnect the EEC PCM electrical connector (see Chapter 4 Section 16 if necessary). 68 Check the resistance between the EVR electrical connector signal return pin and PCM electrical connector pin 33 (see illustration 5.57). Resistance should be less than 5 ohms. If not, service the circuit for open.

69 Check the resistance between the EVR electrical connector signal return pin and around (PCM still disconnected). Resistance
should be greater than 10,000 ohms in both cases. If not, service the circuit for a short to ground.

70 Check for stray voltage at the EVR signal return pin (PCM still disconnected). No voltage should be indicated. If it is, service the circuit for a short to power.

As you look into the harness connector for the EVR with the lock tab on top, the L terminal is hot from the EEC Pwr relay (and goes to almost every other sensor & actuator), and the R goes directly to pin 33 on the EEC.

 

Do you mean the large gray plug connected to distributor? I also see a smaller gray plug connected to the same wiring bundle as the larger plug,is that it? If so should I unplug it while it is running or before I start it? The distributor is not loose.

Regarding the EGR, the equipment I have access to is an OHM meter which is not on me presently so checking the EGR might be out of the question.

I did disconnect a green line at the valve and put my finger over it and I believe I felt suction. I think in regards to checking the EGR, I don't have the necessary gauges and pumps to do that. Do you think that a faulty EGR system would cause my problems?

 

your description sounds almost exactly like the problem i had with a 300 6 cylinder a few months ago. the 3 day old egr controller went bad. took a week to find it because i was to stuborn to check a new part.

 

Okay, I believe I found the spout connector. I unplugged it and there was no change in the idle.

Is this the large gray plug that attaches to the distributor or is it someplace else? I am not exactly sure what the TFI module is and I don't have my Haynes manual with me.