Engine Skip & Peristent Rough Idle

[Kodachrome Wolf]

So the folks that keep up with my Reader's Ride thread, you'll know I've been sorting out some weirdness on the '87 wagon.

I was up at Nick's on Sunday. He said things clearly aren't quite right despite what I've done. He mentioned you can feel a skip in the motor going down the road around 45 MPH in overdrive. It'll miss/skip while decelerating.

So here's where it all started: A few weeks ago while I was up in PA, the wagon went the fastest it's probably gone. The next morning the idle was pretty rough. Drove fine at speed. Changed spark plugs when I got home, not much change occurred. Idle still rough; hesitation and bucking with light throttle at slow speed. Pulled codes, had one for EGR. Cleaned the old one and the passages into the intake. Had no effect, so I replaced the EGR valve and sensor. Had the battery disconnected while I did that to clear codes and reset the ECU. Starting up the car, it idled considerably better, but still runs visibly rough as the engine shakes. Driveability improved and bucking was generally eliminated, but it's still not quite right.

So we move to Sunday at Nick's. I let him take it out and the first thing we got was a whiff of gasoline through the vents on start up. Now I should mention that going WOT at speed usually results in the gas smell for a moment. I've suspected EVAP, but Nick said there could be a fuel injector issue. We looked for any dampness when we returned, but we couldn't see the injectors very well under the intake. As far as the test drive went, the miss/skip was noticed around 45 MPH in O/D. We also checked for codes again and pulled a 34; an EGR code.

Nick tested the EGR solenoid and by depressing it, it significantly affected idle and caused it to stumble really hard.

In general, the idle is better than where I started, but definitely not where it should be. A noticeable skip can be noted below 50 MPH. Interstate speeds make any issues undetectable. There's a gas smell that was noted after the car sat for a little bit. The same smell can be found after a WOT run.


He and I have gotten a small list of things to run through, and of course I'm looking for advice on what to also look at to get things where they should be.

Right now plans are to:
-Check for vacuum leaks
-Plug vacuum lines running to non-functional Thermactor and smog equipment (pump is gutted and there's not even any catalytic converters right now).
-Pull upper intake and swap the injectors using the 4-port, updated style 14 LBS injectors (The current ones are likely the single pintle style with around 320K)
-Get proper spark plug wire spacers installed
-Inspect EGR valve

What else should I be looking for while I'm trying to address these symptoms?

[DerekTheGreat]

I can't remember, but have you verified the timing to be 10* and that the dizzy, PIP & that module thing that mounts to dizzy are OK?

[Kodachrome Wolf]

I can't remember, but have you verified the timing to be 10* and that the dizzy, PIP & that module thing that mounts to dizzy are OK?

The dizzy was set back to it's original position after I swapped the TFI. I marked the base and did everything in car. It ran like normal after changing it. It hasn't given me any of the classic signs of TFI issues and always starts, runs, and doesn't shut off at random.

[Tiggie]

Sounds like you've got a good plan there. I'd add checking the throttle position sensor to the list.

[gadget73]

Did you actually verify the timing though. Possible it was not correct to start with. Also worth checking it just to watch what it does. With that many miles I'd expect slack in the timing chain, which you'll see by watching the timing marks. They will dance around as the chain flops. Ignition and fuel are driven off the distributor so hitching there will make both the injectors and the ignition stutter. I suspect its the fuel that is more noticeable.

34 means the egr valve is partially open or the sensor is wanky. If its all new stuff, confirm the voltage output of the sensor and if it is high, pull the sensor and hit the end of it with a file for a few strokes to see if you can get it where it belongs.

[Tiggie]

Sensor check:



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[TecNickal]

I timed it when I did intake manifold and valve cover gaskets.
That car has a jasper reman on it with...60-70k or so. No oil burning.

Car was set for 10 deg btdc when sold to him. It's still set for that looking at it.

We also assume the aftermarket BWD components are functioning correctly and are using correct values for PCM to understand.

[Kodachrome Wolf]

Did you actually verify the timing though. Possible it was not correct to start with. Also worth checking it just to watch what it does. With that many miles I'd expect slack in the timing chain, which you'll see by watching the timing marks. They will dance around as the chain flops. Ignition and fuel are driven off the distributor so hitching there will make both the injectors and the ignition stutter. I suspect its the fuel that is more noticeable.

34 means the egr valve is partially open or the sensor is wanky. If its all new stuff, confirm the voltage output of the sensor and if it is high, pull the sensor and hit the end of it with a file for a few strokes to see if you can get it where it belongs.

I have not verified timing. I will need to get a timing light since I don't have one. As far as the mileage goes, some things are at 320K, but other things are considerably fresher. Nick says it got a new short block at some point, so the engine only has around 70K, IIRC. I know Nick set the timing before I got it, so I'm not sure if it got out of time somehow. Engine is still pretty tight. However, a number of other things are suspected to be original, like the intake, injectors, etc.

There's a vacuum tree under the intake, correct? If so, I have no idea on the condition of those vacuum lines.

34 was the code from earlier when I first pulled codes a few weeks ago, but unfortunately it's persisting. I did put on a new EGR valve and position sensor. I'll go through the stuff with a multimeter to find the culprit. I did hang onto my old EGR valve and position sensor. I may try swapping position sensors just to see if anything changes there. The old position sensor was clean when I removed it from the old EGR valve.


Tiggie, thanks for the service manual page. I'll have that open when I get out to work on it. I'm going to try and purchase a set of shop manuals for it since I love having that stuff.

[DerekTheGreat]

The dizzy was set back to it's original position after I swapped the TFI. I marked the base and did everything in car. It ran like normal after changing it. It hasn't given me any of the classic signs of TFI issues and always starts, runs, and doesn't shut off at random.

TFI!, that's it! I always forget what the acronym is.. VCV has mentioned that he had a TFI that was wonky and would cause some weird driveability issues. Can't remember if it ever crapped out on him but I think I remember him saying it had a stutter at certain RPMs. He swapped TFI's and the stutter was gone.

[VicCrownVic]

Yeah, I had one TFI module that would cause a miss at high RPM. It went away when I swapped it for another one and came back when I put it back on. Definitely not your typical symptom for a bad TFI module, but may be something to keep in mind if everything else on your list checks out ok.

[gadget73]

both the TFI and the PIP have very non-specific failure modes. "runs stupid" can be a lot of things.

70K shortblock, ok, much better than 320k. I'd still want to watch the timing just in case they used a shitty chain and its gone sloppy. Its probably fine, but I probably should have been rich and good looking too. That didn't work out, but hopefully the chain does for you. What did old Ronnie Raygun say, "trust, but verify" ?

[Kodachrome Wolf]

Actually got some real work done today.

Let me preface my findings with a weird moment where things ran fine. I started the tear down with the wagon under the carport. I had unplugged the EGR and pulled it's vacuum line. I removed the air intake tube from the air cleaner and had unbolted the throttle body. I had also removed the two center bolts from the upper intake. It was at that time I was asked to move the wagon from under the carport, to the lean-to on the shed. I tossed the throttle body back on and only used two bolts to secure it since I was moving a whopping 30 feet total. Firing it up, things were butter smooth. Even in gear it was behaving normally.

Anyway, I still pulled it apart since there's a few things that need attention anyway before they become real issues.

Things are pretty dry. Doesn't look like any injectors leaking, however I still may replace them as a preemptive action.


Oozing heater line. I'll replace this one and the other rigged up line going to the heater core. That'll give me peace of mind for the future.


Kind of hard to see, but the main vacuum line going to the tree is badly cracked in many places, particularly on the bends. While new moulded hose can't be had, running longer lengths of correct diameter hose should prevent kinks allow me to run new lines.


EGR ports on the intake were looking clean, however I did notice more carbon build up on the port behind the throttle body. I took upper intake home with me after I took it off, so I'll take the EGR valve off again and clean it.

The upper intake is going to get cleaned up and painted. I'm going to go with white and red lettering. I'm also going to try and clean up the valve covers by wiping them down in car.

Once I ensure the EGR is clean, vacuum and coolant hoses are replaced, and fresh injectors are installed, I'll get things re-assembled. From there I'll do multi-meter testing on the EGR position sensor and inspect the EGR solenoid further.

[Rodentkiller]

I suggest after you fix the vacuum leaks and if you still have a bad idle find the computer and "slap" the computer if the idle improves you need a computer with a "calibrator".

[Kodachrome Wolf]

I suggest after you fix the vacuum leaks and if you still have a bad idle find the computer and "slap" the computer if the idle improves you need a computer with a "calibrator".

"Percussive Maintenance"


So the MAP vacuum lines are fresh. Date stamped 2013, and they're nice and pliable, no cracks or things like that. The main feed that goes to the three other branches has to be original to the car since it's all Motorcraft branded. I went to remove it from the feed and it snapped in half. A clear indicator fresh hoses are needed.

[gadget73]

That molded one in the picture with the cracks should be the PCV line.