Hunting Idle, Random Stalls, No Power...

[b58tt]

I've gone through most of the surging idle checklist and it none of them have worked. The vehicle randomly stalls out when I go to start it, and I've been told it has an air/fuel ratio of 14.5. I was told that was running too rich.

What could be causing the mustang to be running that rich? I've not done anything to the vehicle, and its sat for a couple years. It's an '88 GT with speed density if that matters.

 

[Aliate X]

did you check your IAC? Had the same problem after my h/c/i swap, the car was surging so bad, replaced the IAC, fixed it 90%, still have a small vaccume leak somewhere.

 

[jrichker]

did you check your IAC? Had the same problem after my h/c/i swap, the car was surging so bad, replaced the IAC, fixed it 90%, still have a small vaccume leak somewhere.

Very good advice.

I've gone through most of the surging idle checklist and it none of them have worked. The vehicle randomly stalls out when I go to start it, and I've been told it has an air/fuel ratio of 14.5. I was told that was running too rich.

What could be causing the mustang to be running that rich? I've not done anything to the vehicle, and its sat for a couple years. It's an '88 GT with speed density if that matters.

What did you get for codes?

Are you sure that there are no vacuum leaks? Replacing all the hard plastic lines with new rubber vacuum hose is always a good idea. I usually break a 1" piece of the hard plastic line off and use it to splice in the fancy rubber connectors.

The 14.5 A/F is very good, 14.7 is perfect.

 

[b58tt]

Please forgive me, but where would I find the IAC?

The car itself is bone stock with the exception of an aftermarket clutch.

Lastly, it does sound like it has a leak, but I can't seem to find it.

 

[joel5.0]

Please forgive me, but where would I find the IAC?

The car itself is bone stock with the exception of an aftermarket clutch.

Lastly, it does sound like it has a leak, but I can't seem to find it.

Side of the throttle body, look for....

and check this article on tips to help you find vacuum leaks. GL

 

[stang&2Birds]

http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

The IAB/IAC gets clogged from Carbon because of the EGR. Also, it gets clogged from dirt. You should only get a new *Ford* IAB/IAC. Sometimes, by using a full can of carb cleaner, you can clean the IAB/IAC.

The IAB/IAC can go bad (stick) within ~50K miles.

 

[795.0pacecar]

Check to make sure the pintle valve in the EGR isn't jammed open by carbon. Mine was jammed open about an 1/8" causing a vacuum leak and a surging idle.

 

[stang&2Birds]

Check to make sure the pintle valve in the EGR isn't jammed open by carbon. Mine was jammed open about an 1/8" causing a vacuum leak and a surging idle.

Yup!!

[on soapbox]
IMHO, 95% of **ALL** idle problems would be fixed by a new *Ford* IAB/IAC AND EGR. Instead, people screw around f**** up the TPS, F***** around with this and that, screwing up this and that, putting in a POS TFI, POS TPS, and so on.

First, read the codes. If there are NOT any codes, SPEND THE F********* $100 on a car that is 15+ years old, and get NEW AND GOOD *FORD* IAB and EGR! **THEN**, you start to look for other things.

Of course, if you have some new mods, that's something else. Also, REPLACE 02's after ~40K miles, NO IF's AND's or BUT's. For one thing, you get better mileage and lower smog (for the sniffer tests).

But, what will MOST of the people do? Well, they F*********** around with the TPS (which does NOTHING AT ALL FOR IDLE!), then screw around with the TPS some more, then screw around with the TPS some more, then screw around with the TPS some more. See a pattern.
[off soapbox]


Also, make sure the timing is correct. If it's very advanced, you can have some idle problems.

 

[stang&2Birds]

I've gone through most of the surging idle checklist and it none of them have worked. The vehicle randomly stalls out when I go to start it, and I've been told it has an air/fuel ratio of 14.5. I was told that was running too rich.

What could be causing the mustang to be running that rich? I've not done anything to the vehicle, and its sat for a couple years. It's an '88 GT with speed density if that matters.

Read the codes. Or junk the car. If the car is running rich, you have problems. Could be a ton of stuff. Get a code reader, fix the problems, or just save yourself time and money and junk the car.

Hmm, junk the car, or $20-$100 for a code reader. Seems like a hard choice, huh?


BTW: You could have bad O2's, MAP, vacuum line(s), wiring, or many other things. Any of those will cause a SD EFI to run rich.

 

[stang&2Birds]

The best scanner that I know of for a decent cost is the one with an LCD readout.

On ebay, do a search for
Digital FORD Code Reader

View attachment 458475

SOME Wal_marts, Sears, parts places may have it in stock. Or, look for it else where on the web. It's much easier to use than the beeping and LED readers.

That's the one I use the most. I also have an autoXray ezscan 6000, and a "few" other scanners. I paid over $600 for my 6000. Now, there's a place on ebay that has it for ~$500. But, you can't datalog a Fox Stang, so for ~$150, you can get one with similar abilities (text readout) for a Fox Stang and save yourself a lot of money.

Do an ebay search for
scantool
CP9110

You should be able to get one for ~$100. Make sure you get the FORD cartridge and cable.

Yea, I have a CP9100 also. In fact, I have two of those and two of the simple LCD code readers. Plus, a number of others.

 

[b58tt]

I've just disconnected the IAC/IAB cable.. is the car supposed to be able to start with this cable not connected? Becasue the GT won't start at all now heh.

 

[jrichker]

I've just disconnected the IAC/IAB cable.. is the car supposed to be able to start with this cable not connected? Becasue the GT won't start at all now heh.

No working IAC should be a no start condition. The IAC is supposed to open during cranking to provide airflow for the engine. Occasionally someone will have changed the throttle stop screw to set the idle. That bypasses the IAC and sometimes it is enough airflow to start the engine.

 

[stang&2Birds]

I've just disconnected the IAC/IAB cable.. is the car supposed to be able to start with this cable not connected? Because the GT won't start at all now heh.

Yes and no. With the IAB/IAC not connected, and with a *warm* engine, the engine "should" idle around 500 rpms. But, the idle adjust screw isn't always set right, many engines will not idle that low, some engines need some throttle to start and stabilize, and so on.

As much as it's WRONG to disconnect ANY sensor or control while the EEC is "on", you may have to start the engine, let it warm up, then unplug the IAC/IAB.

There's an idle speed set procedure posted somewhere. It may be in the tech section here or on the corral. With the exception of the WRONG advice to "adjust" the TPS, it says what to do.

Regardless, if your car idles by itself, then that is NOT your problem. The idle speed set procedure is to make sure that the IAB/IAC has a wide enough range to control the idle/"throttle" speed.

 

[b58tt]

I don't want to bother you, but do you have an instant messenging program i can contact you through?

 

[jrichker]

There's an idle speed set procedure posted somewhere. It may be in the tech section here or on the corral. With the exception of the WRONG advice to "adjust" the TPS, it says what to do.

I am the author of that tech note. The advice to adjust the TPS was primarily to keep the TPS voltage from exceeding the 1 volt mark and getting into the Run range of TPS voltages.

See http://forums.stangnet.com/showthread.php?t=534062 for more. Your comments and suggestions for sucessful solutions are welcomed. Post them there or PM them to me.

Joe R.

 

[b58tt]

hey guys, i just found this out.

anyways i disconnected the IAC/IAB or whatever, cleaned it with carb cleaner, reconnected and started the car up.. it stil shot up to 2000 RPM, and even at one point shot up till 3000 RPM

anywaysa once the car was fully warmed up.. i disconnected the IAC and it idled like a kitten.. so perfect.. does tihs mean i need a new IAC?

I mean the idle w/o the IAC was 600 rpms roughly..

 

[stang&2Birds]

I am the author of that tech note. The advice to adjust the TPS was primarily to keep the TPS voltage from exceeding the 1 volt mark and getting into the Run range of TPS voltages.

See http://forums.stangnet.com/showthread.php?t=534062 for more. Your comments and suggestions for successful solutions are welcomed. Post them there or PM them to me.

Joe R.

I didn't mention any article specifically.

However, in your article you mention that "magic" voltage of 0.98v. Sorry, that does not exist. As long as the TPS is between ~1.1 v and 0.6v, at idle, it does not make any difference.

Your article:
4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

My TPS FAQ:
http://www.veryuseful.com/mustang/tech/engine/Mustang-TPS-FAQ.html


Joe: It would be GREAT if you could update your article. It's an uphill battle getting the correct information about the TPS and how it's really used in the EEC.

Yes, I've read the Ford strategy documents (~400 pages for the "A9L"), and I've looked at the code. Some of the Ford strategy documents are on "the yahoo site". Since Ford has been nice enough to let them stay, I do NOT talk much about them. They do have a lot of proprietary information in them.

I'm one of the few people who *used* to modify the EEC code. I even checked on the SD EEC's to make sure that they flag and indicate a TPS out of range error. On my car, I can go between SD, MAF, and GM MAF with only a an ~hour+ of work.

 

[stang&2Birds]

hey guys, i just found this out.

anyways i disconnected the IAC/IAB or whatever, cleaned it with carb cleaner, reconnected and started the car up.. it stil shot up to 2000 RPM, and even at one point shot up till 3000 RPM

anyways once the car was fully warmed up.. i disconnected the IAC and it idled like a kitten.. so perfect.. does this mean i need a new IAC?

I mean the idle w/o the IAC was 600 rpms roughly..

Sorry, no IM or PMs. I'd get swamped.

If you have over ~50K miles or 7 years on the IAC, then get a new *FORD* IAC. Do NOT waste your money on the junk they sell at the parts store. They "may" work for a short time. It's hard enough for a well made IAC to survive in the Stang setup. Put on a cheap one, and it can go "quickly".

Unless you're planning on fixing it and selling it right away, get a *FORD* IAC/IAB. The same is true for the EGR, TPS, and TFI. It's your money and time, I'm trying to save you both.

 

[stang&2Birds]

I am the author of that tech note.

GREAT tech article!

There is one important thing that I don't see mentioned - Check the timing. The EEC uses the timing as the main way to control idle speed. The timing is a fine and quick adjust, and the IAC is a course/slow adjust.

If someone has their timing very advanced or retarded, then when the EEC advances or retards the timing to speed-up/slow-down the idle speed, the rpms will "burp" because of stumble (too much advance or retard for the engine). That can cause the EEC to add/subtract more timing and to start adjusting the IAC. Then, you get the surge.

IMHO, having the timing "within spec", having a *good* IAC, and having a fully closed EGR should cure ~95% of all surging issues that are not related any engine mods.

When people put on cone filters, engine bay air filter, cold air intakes, different MAFs, change the air intake path (filter to intake) at all, and so on, then there are other many other issues that can cause surging.

 

[b58tt]

Well, I don't think its the IAC.

I installed the IAC and the car idled to 600 RPMS which was great, but then shot up to 3000 RPMs. This is a bit different from the normally starting at 2000 RPMS and going up to 3000 RPMS.

I'm kinda stumped at this point.

Does anybody have a picture of the IDLE screw underneath the throttlebody? And exactly where is its normal position for a normal idle? Right now it idles at 600 RPMS w/o the IAC connected and fully warmed up.

Lastly, how does go about checking timing?