Idle issues when hot

[danco86]

I've been dealing with a hot start/idle issur that has been getting progressively worse.
Starts great cold and runs/idles fine.
Once it is hot and I go to start it, it fires right up no problem, but if I don't give it gas right away, it won't catch idle, then it quits. Every time. If I give it gas, it'll idle. Sometimes if idling to long, it'll all of a sudden start hunting around, then quit.
Lately, it has started to stall when I come to a stop once in awhile.
It drives fine and throttle response is good. Problem is only at idle.
Sounds like TFI symptoms, but not sure. Any ideas before I take the TFI off to get it checked?

[84GT350CONV]

You may need to supply us additional information. Like have you hooked a code reader up to it? Is it an original fuel injection system and so on. It could be a throttle position sensor, coolant temperature sensor or something like that, but without additional information it's hard to help you.

[danco86]

Original fuel injection.
MAF conversion, A9L computer.
Yes, had a code reader on it. No codes at all. But after it finished doing its self test, the idle started hunting right away.
The tps is good. Also confirmed the AIC motor is good as well.
Going to borrow my buddy's tfi tester tomorrow.

[danco86]

Double post

[84GT350CONV]

Consider a vacuum leak also.

[danco86]

I've looked and looked for a vac leak, but everything appears fine. Used the dreaded intake cleaner procedure with hose and fire extinguisher by my side. Checked all hoses, injectors bases, gaskets etc.
Pulled the hose from the tb to oil filler neck and covered the open end with my thumb with the other end still attached to the filler, felt good vacuum build, so appears there is no leak at the crankcase end.
The tfi tested good. Even tried another one that was laying around just to be sure.
Tps is at 1.004V and is steady and responsive.
I did a base idle set by disconnecting the AIC and then disconnected the battery etc.
Now when it is hot, it won't catch idle on the first start attempt as before, but on the second try it will start and hold idle. That is new.
However it still sporadically hunts around and will stall when idling. It will also sometimes stall when clutching in and out, like in stop and go scenarios (parking lots and the like)
I am at a loss. Getting frustrated.

[bwguardian]

Not very savy with FI cars but have you checked the O2 sensors...

[danco86]

You bet. Both are brand new. The ecu will give a code if the O2 sensor is not sending inputs.

[Jerry peachuer]

If it was vac leak it would idle up FYI efi car
If it's carb it will hunt or stall I know yours is not carb
Don't get frustrated your going to possibly help out many other people

I would look into fuel side of things
Does it clear up when rev ing it out of the idle hunt? If so see if it's black smoke
What's the engine temp looking like when it acts up

[grabbergreen84]

Try unplugging your MAF, and see how it idles, and then take it for a drive. If the problem is gone, then try cleaning your MAF sensor. Go to the parts store and get the proper CRC Quick Drying Electronic Cleaner. You'll need some torx security bits to remove the 'sensor' itself from the meter housing, then just spray it down. If you're careful and steady, I guess you could dab at it with a Q-tip or something too. Don't use brake parts cleaner or carb cleaner. Hopefully that will straighten it up.

Your symptoms sound a lot like mine. I cleaned my 70mm MAF, and put it back on, and it started doing it again. So I threw my stocker on, and it runs perfect!
Plus, my problem didn't show up until immediately after I put my new heads on, so I ended up on a real wild goose chase. The MAF was the last thing I suspected. When I unplugged it at an idle, it ran worse, so I kept chasing elsewhere. Finally, I unplugged it and drove it, and had finally found my problem.

Also inspect and check your TAB and TAD solenoids for cracks/leaks. And check operation of the Bypass and Diverter valves themselves.


Or, is it possible that your balancer has slipped, giving you an erroneous ignition timing reading?

[bwguardian]

danco86, I just went through your build thread...wow! You don't state which air filter you are running in the car. Is it a K&N or paper filter?

[danco86]

Thanks for the input, guys.
I do want to get to the bottom of this and provide an answer to this thread. I've done a ton of searches here and on the corral, and almost all of them never end up saying what the problem ended up being.
I was pretty sure it wasn't vacuum, but needed to rule it out. Definitely never idles high or hangs up.
The fact that it is so inconsistent makes it really hard to determine the problem.
I was thinking the MAF next, but didn't know how to go about checking it short of graphing it at a tune shop. So thanks, I'll try that.
I still have to check fuel pressure, but it is the original fpr. The fuel pump is a new 195 LPH. I just figured they either work or they don't.

I am running a k&n filter in the factory air box.

[bwguardian]

I am running a k&n filter in the factory air box.

This is most, if not all of your problem. The oil on these filters, especially when over oiled, soaks the sensors not allowing them to function properly. Switch back to a paper element, clean everything up as mentioned above, and see what happens. I have seen this time and time again with fuel injected cars. I run the K&N's in all my vehicles but they are diesels and carb engines without all the sensors on the intake side.

[danco86]

I have not looked at the intake tube or MAF sensor since the initial startup. I did oil the filter lightly. I have run them in my diesels as well.
The car does demand more air now, and even thought it has had a k&n in it since the 80's, it was speed density until now.
Fingers crossed it may be that simple.

[danco86]

Ok, so I took my MAF sensor and housing off and checked them for contamination. Both were clean and dry as a bone. There does not appear to be any oil residues from my k&n filter anywhere along the intake ducting. I do know what you are talking about with over oiling though, bw. I over oiled the k&n in my 7.3 once and I could see it track all the way towards to the turbo.
I cleaned the sensor off anyways with crc contact cleaner and reinstalled everything. No change. Still wouldn't catch idle on the first hot start, then stalled on me as I pulled into the grocery store parking lot.
So on my way home I stopped into an empty parking lot and disconnected the MAF sensor. The car idled bouncing steadily between 600-800 rpm. Drove it around a little bit, ran fine, didn't stall. I then stopped and started the car numerous times, giving different time intervals between starts. The car started and caught idle every time without having to give it gas. It still hunted steady at idle the whole time the MAF was unplugged, but did not stall.
Does that sound like how the car should run with the MAF disconnected?
I am hoping that this May have been my issue the whole time. Just don't want to get my hopes up yet.

Jerry, yes it does clear up if I gas it when hunting (MAF connected), or at start up before it gets a chance to stall. No black smoke.

[grabbergreen84]

Does that sound like how the car should run with the MAF disconnected?
I am hoping that this May have been my issue the whole time. Just don't want to get my hopes up yet.

Sounds just like mine. Do you have any friends with MAF 5.0s? My next step would be to try a (borrowed) known good MAF, and see if it cures it.

Mine never really hunted though. It would backfire when floored, and was more difficult to cold start, but it idled OK. As far as the hunting, I would check the plug wires, and the battery terminals/connections first. I've seen both of those cause a hunt.

When I was chasing the problem, I was adjusting timing and fuel pressure constantly, switching between distributors, and I even threw a new fuel pump and plug wires at it - it definitely needed the wires.

[danco86]

I've got a MAF lined up from a buddy. I'm back to work tomorrow & my days are 15 hrs. with the commute, so it'll be the weekend before I really get to it again.
I'll get my timing light on it and a fuel pressure guage too. I know I had the timing set right to begin with, but I've never checked the fuel Pressure. The insurance comes off the car in a little over a month. Would be nice to put it away with all the bugs worked out of it for the winter.

[danco86]

Update:
Borrowed a MAF sensor from my buddy. Swapped it out and..no change.
Still the same old symptoms.
I'm kind of ruling out a fuel issue because when I unplug the MAF sensor, the car starts and catches idle every time.
So, not sure what to try next.
Suggestions?

[grabbergreen84]

Are you sure that the O2 sensor harness is routed to the proper side(s) of the exhaust?
If the right-side connector is plugged into the left-side sensor, and vice-versa, it will confuse the heck out of the computer.


Maybe it wants a little more fuel pressure, but that would entail a new regulator.

[grabbergreen84]

Also, I'm reading your build thread to see if I catch anything.

Amazing looking car! Top-notch work!

[danco86]

Hey thanks for the compliment, and for your help!
The O2 harness is definitely the right way, the low oil level sensor is in the same harness, so it only goes the one way.
I have access to another a9l ecu to try. I'll also check my vss wires etc at the same time. But with no codes, I'm sure that they're fine.

[grabbergreen84]

I didn't realize '86s got the low oil lever sensor.

Going back and rechecking the MAF conversion wiring is a good next step. Go ahead and double-check that that SVO plug-in adapter really does correspond to the computer's and car's pinouts as well.
I might be crazy, but I think I remember once reading here, that those plug-ins didn't match the fox passenger-car pin-out scheme, but I might be thinking out my arse here too.

I know that when I converted my '88, I initially got one of the MAF wires pinned wrong, and it ran worse than yours sounds to be. Luckily I didn't fry my EEC...
Went back the next night and found my error, fixed it, and never looked back.

Also, maybe whoever loaned you the other MAF, will let you try their distributor in your car too. A bad PIP will cause some weird hard-to-diagnose problems, as well.

[eight666lx]

theres a great thread out on a different site called "help me create the surging idle checklist" i cant get the link (weird phone internet format) but if you google those words and maybe some keywords like foxbody etc. .... you'll find it easily. its packed with info and is written for efi cars. its got a bunch of electrical info, measurements n such.
it may help, good luck

[danco86]

That thread is on stangnet. And yes, it is an awesome thread.
It's a lot to root through, mine seems to have a lot of those symptoms, except it is fine at cold start. All the issues rear at operating temp. The car is stalling all the time now when approaching to a stop. The fact that it has been getting progressively worse just adds to things. I just have to try things one at a time as time permits. Would be nice to be able to narrow down the list.
It sounds a lot like vss, but no codes and the fact that it gets worse doesn't jive. Also, the inability to catch idle at hot start seems to point somewhere else.
It was fairly easy to drive thru the problems initially, but with it stalling so often now, I'm pretty much done driving it around town til I get this figured..

[bwguardian]

Take a look at this http://vb.foureyedpride.com/showthre...ght=86+bucking thread as there may be some useful information for you in it. I linked the last page where he was able to solve the problem but you can go through it if need be.