Engine Skip & Peristent Rough Idle

[Kodachrome Wolf]

TFI? PIP?

Just cause it's new doesn't mean it's good...

It's under warranty... I could try swapping it out. I'll order the Motorcraft one and replace the BWD one since the price difference isn't huge.

[gadget73]

and is the iac in good working shape? Do the temperature sensors have a reasonable reading with the engine warmed up?

http://www.grandmarq.net/oldfuelinjection/page10.html

[Kodachrome Wolf]

and is the iac in good working shape? Do the temperature sensors have a reasonable reading with the engine warmed up?

http://www.grandmarq.net/oldfuelinjection/page10.html

I assume the IAC is functioning normally. I've never heard the "foghorn" noise that they supposedly make when failing nor have I ever experienced a no-idle condition. It has always idled, back when it was normal, and even now.

I would need to measure the ECT since I haven't done so.


Now this next bit is going to be way out in left field, but only because I've let my mind wander while thinking about what would cause poor idling and the miss. Considering the engine was put under some serious load to travel at rather high speed, would it be possible that somehow maybe a rocker arm shifted, or would that make a way too obvious issue?

[gadget73]

The aeros make the foghorn noise. Box ones can get sticky and cause a rolling or uneven idle or stalling when shifting gears. Non-OE ones can't always control the idle correctly either. I've personally run a self-test that gave codes for unable to control idle too high and too low at the same time. Installing an old Motorshaft part made both issues stop. Often you can just pull them and flush it out to restore proper operation.

If the rocker shifted completely or broke you'd have a dead miss. If something went slightly wrong you'd have a very distinct tap noise from the lack of preload in the valvetrain. If the valvetrain is quiet its probably fine. Not an absolute guarantee but usually valvetrain issues are audible before they cause running problems. Mine was running for too long with a cam that had extreme wear, cracked lifters, worn rockers and a couple bent pushrods and it didn't misfire. It sounded like a box of marbles being shaken rapidly but it ran fine.

[DerekTheGreat]

I didn't have good luck with the new IAC I bought, supposedly Motorcraft as well. I had great luck though, with the junkyard unit I pulled & reconditioned. BWD has a reputation of "Broken When Delivered" so new in box is not equal to "good in box."

[VicCrownVic]

I have a non original IAC on The Scab that I found in my dad's basement. I have no idea what it is off of, it's definitely not a box IAC, but it started making the foghorn noise a few days ago. I'll have to post a video when I get a chance. It only does it on hot restarts, like when I shut the car off to go grab something real quick then start it again.

[DerekTheGreat]

I'd like to hear that.

[VicCrownVic]

Link to the video I took yesterday after getting home from work:

https://www.flickr.com/photos/131643349@N05/36074932140/in/album-72157687426947075/

It started out a week or two ago only doing it for like a second, then the last few days it has been going long enough to get the video.
I didn't bother to look into it right away since, until a couple days ago, it wasn't doing it long enough to figure out where it was coming from and I haven't noticed any running problems. Then coincidentally KW posted about this foghorn noise so I checked it out and it does seem to be coming from the IAC area. I figured it sounded like something vacuum related getting stuck, but wasn't sure what it was until I saw that post.

EDIT:
In all my years driving box panthers (with box IACs, not whatever I have on this one) I've never heard such a noise and have changed plenty of IACs.

[DerekTheGreat]

Wow yep, that really does sound like a fog horn. Wonder why, is it the stepper motor going bad?

[BigMerc96]

That is what I assume is causing it. The stepper motor gets a dead spot, so it sits there bouncing the valve around making that noise. Its a really common symptom on a '96-'02 Panther, something about the design causes them to do that. I've heard a few make that noise, the one from my '97 would occasionally but worked fine for quite some time after that started. Eventually I started getting inconsistent idle and occasional stalling so I broke down and got a new Hitachi part since Hitachi is the OE for the aero/whale style IAC.

[Kodachrome Wolf]

Finally got back out to the wagon today. I grabbed two sensors from work yesterday, just to have them on hand if I needed them. I checked the coolant temperature sensor and the manifold air temperature sensor. Coolant temperature sensor was giving me weird values, so I considered it suspect. I went ahead and disconnected the battery and got started. The manifold air temperature sensor's body had been broken off sometime in the past, so I just replaced it along with the coolant temperature sensor. I believe both are original, however how original, I'm not sure. They may be the 1987 originals, or they may have been the ones that could have possibly been on the replacement engine.

Now FWIW, I purposely left the EGR block off in place just to keep that out of the equation at this point. I hooked up the battery and cranked up the car. Seemed to be running considerably better, so I took it on a short drive to get it up to operating temperature. I really couldn't feel any missing as I could before at light throttle, however I didn't take a very long route, maybe a mile at most. Once I was back in the yard, I put it in drive and applied the brakes and just allowed it to stand. It seems to be running better. It did not start stumbling and missing hard as it did before, nor did it stutter when it got light throttle from a stop. It also did not exhibit the "idle gets worse the longer I keep the brakes applied" symptoms that had been affecting me. Now, I did note a slight miss feeling every once in a while while it was in drive and stopped, but not in the way it was behaving before with the erratic idle (it may have always done that and I never paid much attention to it).

I'm going to continue to monitor it for other symptoms and re-introduce the EGR back to the mix and see if anything else changes. It is very possible that coolant temperature sensor may have gone bad given what I was reading on the voltmeter, assuming I was doing it correctly based on the information I could find on the internet.

[gadget73]

The speed density system really needs temperature input for accurate fuel metering. It has a lot to do with the "density" part of the equation. If the ECT doesn't get to a certain temperature, the oxygen sensors never turn on. If the ACT doesn't hit the right temperature, the long term learning strategy doesn't work either. These really don't have a whole lot of data input to the computer, so it really needs all of it to be correct in order for it to work right.

[Kodachrome Wolf]

So I was able to drive a longer distance today since I am using the wagon this week which makes it considerably easier to work on it. It got right back to its stupid games waiting in traffic. The bucking and missing at low RPMs is very reminiscent of when the TFI module crapped out on me, except obviously it's running. I recall when the TFI went bad, if I accelerated hard enough, it would clear up, but mid range and low starts it wanted to stutter, before shutting off.

TFI? PIP?

Just cause it's new doesn't mean it's good...

I'm still considering swapping the TFI out with a Motorcraft one. I'm wondering if the current one has heat damage to some extent, since only low RPM operation is affected, yet under normal acceleration and moderate cruising speed (above 1800 RPM), there's no issues.

[Kodachrome Wolf]

I think there's a possibility that's being closed in on. I've been looking up PIP issues on other Ford forums with people that have 302s (namely trucks and Mustangs). Based on what I was seeing, I decided to check to see how it ran with the SPOUT unplugged. Big difference there in driveability. It doesn't go stupid at idle (still a bit touchy, but not like before) and light throttle applications while cruising in OD did not result in the bucking trying to get the RPMs up. Also, it did not miss and sputter on deceleration.

I haven't a clue how old the distributor is. It may be the original unit with 320K on the thing. If the PIP is original, it's possible it's going flaky. I'd sure like to see what it's putting out on an oscilloscope, but dropping in a replacement distributor will be simpler given a time constraint since I'm going to mark everything so that hopefully it'll drop in in the same alignment the old one comes out at, that way I won't have to play around with setting the timing. I'll grab a unit from work probably tomorrow.

If things clear up with a replacement and the SPOUT reconnected, I'll be happy. Either way, I will post results. I hate leaving hanging threads on driveability problems, since someone will likely get themselves into a similar spot someday.

[Kodachrome Wolf]

Just got done tossing in a new distributor and aligning the rotor to my marks on the old cap. Car runs great now. The old PIP was definitely flaking out. Car runs strong now.

I'll hang onto the old distributor for a rebuild.