Idle stumble issue and weirdly quick starts...advice?

[monkeyodeath]

Trying to track down an issue w/ my '86 (3.2).

More than a year ago, I started to have a very sporadic engine issue. The engine would very briefly die and then immediately come back.

This would only happen at really low speeds, like pulling away at a stop like or accelerating in 2nd gear. Never really happened when pulling hard at higher speeds.

I also noticed that the engine would always start immediately after I turned the key, even if it had been sitting for a few days. Sometimes, I'd even hear a brief lugging/pinging sound, as if was starting so quickly the ignition wasn't keeping up. Unexpected and a bit odd for a 34 year old car.

Last week, the car became difficult to start -- would crank to life immediately and die just as quickly.

Did some research and it seemed very likely that the FPR was stuck closed, so I replaced that.

The change did seem to have some effect - the car starts more normally now, after a few cranks of the starter. But now I have a stumbling idle -- every couple minutes, the engine speed will drop briefly, then come back to life, revving up a little bit before settling back to idle speed.

I haven't driven it yet to see if the stumble persists at low speeds -- a little afraid of getting stranded somewhere.

Fuel pressure tests within bounds, and I notice that when the engine dies, the fuel pressure does not really fluctuate -- leading me to believe it's not a fuel issue or an issue with the DME Relay (which is a new Focus 9 unit).

Also, the ICV buzzes and I notice that the idle speed ticks up briefly after the car dies -- indicating that the ICV is trying to raise the idle speed when it senses it dropping. So I feel like the ICV is okay.

Haven't done a full smoke test on the intake yet but did probe around a bit with a can of carb cleaner and didn't find anything. Would seem odd to me that an intake leak would only sporadically affect the engine while sitting still.

Back when I was trying to diagnose the no-start issue, I tried both disconnecting the CHT and jumpering it, and neither seemed to make a difference. I do have the single-wire version though, so I just bought a 2-wire version and plan to install it soon.

I'll also add that I passed a smog test a couple weeks ago with pretty good numbers, so I don't think something is seriously out of whack.

Any thoughts? Ignition problem? Weak coil? Just not sure how to test such a sporadic thing. I know my ignition wires are probably due for replacement, but would that cause an issue like this? Trying to avoid tossing parts at it.

Apologies for being so verbose, but figured adding all the details might help solve the mystery.

[monkeyodeath]

Also, just checked the check valve and it failed, so I really do think something was up with the FPR -- otherwise, how would the thing have consistently started so dang quickly?

[RedCoupe]

If it were me, I'd deal with one system at a time. Once your fuel pressure numbers are where you want them, I'd concentrate on making sure that the ignition system is in good shape. Then, if it is still sporadically acting up, I'd investigate the air flow meter. There has been much written in the forum about how to make a new track for the finger on the potentiometer. Good luck!

[monkeyodeath]

Just went through the car and replaced a few deferred things that needed to be done anyway -- built new spark plug wires (used the same ends but they tested good), new cap and rotor. Replaced the CHT with a 2-wire model and did the reference sensors while I was still in there (insulation on those wires was totally gone).

Still have a weird stumbling idle. As the car warms up it gets to the point where it is really hard to start and won't stay running for more than a few seconds.

Was considering replacing the O2 sensor as it's pretty old at this point (actually have a spare Bosch unit I picked up on sale a couple years ago), but these issues are happening at cold startup, which makes me doubt the O2's influence.

Edit: unplugged the O2 and it had no effect.

Really weird as the car was running fine and passed smog very nicely just a few weeks ago.

The car's stumble isn't like a misfire, it's like it's completely dying very briefly before reviving.

When it dies, the fuel pressure seems to very briefly dip, but I can't tell if that's the cause or the engine dying and the pump switching off.

Starting to wonder if it's the fuel pump. Wondering if the stuck-closed FPR was making up for a weak pump by keeping high pressure in the rail. Now that the FPR is acting normal, small fluctuations in the fuel pump's pressure are enough to bog the engine.

Would be a weird fuel pump failure though. Usually just had them quit entirely.

[monkeyodeath]

Just smoke tested the intake pretty thoroughly, and didn't see anything (figured maybe the intake gaskets were leaking). ICV seems to move freely and operate correctly. Idle switch is good.

I realize this is kind of a boring topic for most but would love some advice as I feel like I'm starting to get down the list of things to try.

I haven't done a fuel flow test on the fuel pump but the pressure appears okay. It dips when the car stumbles and I can't figure out if the dip is a failing pump or the pump getting shut off when the car stumbles. The check valve is pretty weak but I was under the impression that it was only to speed up hot starts. The coil is an original black one.

[911obgyn]

Clean the grounds on the engine, firewall, and the transmission strap. Use a bit of dielectric grease to keep corrosion at bay.
Check fuel air mixture before the cat. You can check O2 sensor with a multimeter should dither around .6 mv if sensor and mixture is ok when warm. But you are right that it will not affect idle on warmup in closed loop.

[monkeyodeath]

Good call. Actually I've found that the car runs even worse when it warms up, and having the O2 disconnected doesn't make a difference.

Swore it had to be an intake leak, but 45 minutes with a smoke machine and a can of carb cleaner (when I could get it to run for more than a couple seconds) yielded nothing.

[911obgyn]

I bought a wideband meter and o2 sensor to adjust mine after fixing intake gaskets that had been tuned around. Took a couple of hours of tweaking afm and idle speed to get it stabilized. Followed bently manual and put a leash on the allen key after dropping it a couple of times and fishing it out with a magnet.

[monkeyodeath]

Dang, you really think I gotta mess with the AFM? I hate screwing around with it, especially with CA smog. Just mystified as to what went wrong in the space of 2 weeks.

I can see the wideband O2 being useful to just see if I'm rich or lean.

Was wondering if it might be an injector or a plug, but it's not really a miss. It's like something pulls the rug out from under the engine at idle and it almost dies. (Or, when it's a little warm, just dies completely).

[911obgyn]

Check idle switch to make sure its clicking, check your stop on the throttle butterfly, clean your IAC valve. No need to adjust afm yet.if idle isnt set right it will hunt and die do the easy stuff first, check plug gaps if you havent if they are way off DME cannot correct timing.

[monkeyodeath]

Idle switch checks out, cleaned IAC and it seems to work fine. Idle doesn't really hunt around as much as just suddenly bog and die or almost die. Sounds and runs normal until that point.

Will check plug gaps but seems odd that they'd be fine one week and bad enough to kill the car the next.

Fuel filter is new within a couple years.

[monkeyodeath]

So I think I've made more progress.

Pretty sure that the fuel pump is not the issue. Jumpered the relay and noticed that the pressure never drops, even when the car stumbles. So the stumble isn't being caused by an FP that's browning out.

What I notice when the car stumbles is that I hear the definite hissing sound of a miss. When I'm revving the engine, I can't really hear or feel a miss, but I do notice the occasional strong puff of exhaust if I put my hand near it.

I'm thinking either one cylinder isn't getting consistent spark or the injector is stuck. Thinking maybe an IR thermometer might help -- find the cooler cylinder.

Though the miss is so occasional it might be hard to find.

Wonder if it might be a clogged injector that was limping along back when the FPR was stuck high. Now that fuel pressure is back to normal, it's dribbling enough to mess up combustion every once in a while.

[911obgyn]

You can do a clean on the injectors with a10cc syringe a 9v battery some wire and a couple of cans of carb cleaner. The O ring on the injector fits the barrel of the syringe, the red tube fits the small end, pressurise with carb cleaner and click the injector on and off with a momentary switch till it is better. Get new orings and rubber bits to reinstall. Use the proper saftety equipment
No smoking or open flame!
Or just send them out.

[monkeyodeath]

Well, I'm thoroughly stumped by this one.

Thinking that I might have just gotten a bad tank of gas, I took a drive tonight. The car had trouble idling at first and there were some hard shudders, with the engine cutting out. But once I got onto the freeway everything seemed fine. Engine pulled like normal.

Then, as the car warmed up, I noticed the occasional hesitation. Very brief shudders while cruising along at 70 in 5th gear.

So, to summarize:

- Hesitates badly at cold start, shuddering and dying at idle. Applying throttle helps keep it going through the shudders.
- Idle speed is fine when it's stable.
- Hesitation is like a total engine thing, not a single misfire.
- When driving at low speeds while engine is cold -- hard hesitations until up around 3k RPM.
- Runs fine at freeway speeds but slight hesitations once warmed up. Seemed to happen most cruising along at 70 in 5th.
- Once I got home, the warmed-up car idled much better, no hesitation or dying.
- Doesn't seem related to physical position of car (bumps, turns, up or downhill)


Replaced:
- Plug Wires
- Cap/Rotor
- FPR
- Reference/Flywheel sensors
- CHT
- DME Relay
- Smoke tested for intake leaks
- Idle switch tests OK
- Fuel Pressure tests OK (haven't done volume test)

Any place else I should look? This feels like an engine-wide failure -- not just a single cylinder misfiring. Wondering if the fuel pump is on its way out, or it's something with the coil or DME. I just hate throwing parts and $$ at the car. Maybe I just need to run through this tank of gas?

[techman1]

It sounds you have everything checked except the actual dme.

Possible to have a connection local you can try a swap?

[monkeyodeath]

Just fired up the car this morning, when things had warmed up a bit. More stable idle right off the bat, still hesitating, but only died once.

Before the car warmed up, I sat and held the throttle at 2.5k RPM. I noticed that the engine speed oscillated up and down maybe 50RPM as I held the throttle in place. Is this an indication of anything?

[monkeyodeath]

Originally Posted by techman1

It sounds you have everything checked except the actual dme.

Possible to have a connection local you can try a swap?

Yeah, might be getting to that point.

[911obgyn]

Perhaps a bottle of techron thrown into a half a tank of gas and an italian tuneup.
A good thrashing for an hour or so may help. It always makes me feel better.

[monkeyodeath]

So I convinced myself that I needed to replace my intake gaskets, as it seemed like a common issue on 3.2 engines that caused similar problems to what I'm experiencing.

Took the opportunity to take care of a bunch of deferred maintenance. Resealed the Triangle area, replaced vacuum hoses, rebuilt the fuel lines with new hose, and had the injectors cleaned.

I kind of regret replacing the intake gaskets, it was a huge PITA job and none of them had been sucked into the intake, so I don't think that was my problem.

Naturally, the stumbling issue persists. On a cold start, the engine fires up fine, but with an idle that stumbles and occasionally dies.

The car also seems to have trouble in low gears and low revs when it's cold. Main time I notice it hesitating is when I have just shifted into 2nd and I'm trying to pull away, or while in 1st. Big stumble and momentary shudder.

Car runs fine at >3000 RPM.

Once the car is warm the engine has a stable idle, and hesitates much less frequently when pulling away in 2nd, though it still happens sometimes. Previously I was noticing a very slight, occasional stumble when cruising in 5th, but not recently.

Happy that the car runs and drives, but would still really like to figure out this problem. Fuel pump? AFM? DME?

Wondering if I'm at the point where I should put a WBO on this thing and get some numbers on how it's running at idle.

[jlex]

Double check that idle speed. Almost sounds like that IAC is acting up.