Fox Will Barely Idle

RockHill · Oct 22, 2016

Just like the title says my 1993 Mustang Lx will barely idle when and if it cranks at all. No throttle response at all. Replaced fuel pump has 42 lbs at the rail, swapped distributors, swapped computer, swapped MAF, checked all fuses. I was upgrading car to 30 lbs injectors and meter and the car was running great went to try out new upgrade and less than a mile into it the car shut off. Trailered it back home and have been scratching my head since. Swapped the injectors and MAF back to stock and still no throttle and will barley idle if it starts at all. PLEASE HELP!!!!

jrichker · Oct 22, 2016

@RockHill

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 200,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

RockHill · Oct 22, 2016

I've been through both of those list (surging Idle and crank and no start) the car starts just hard to start. I can solve the idle problem using the checklist but the car will not rev past 700-1000 rpms. If you press the throttle the car only responds by cutting off or barely revving and I mean lucky if it goes to 1000 rpms. You can disconnect the tps, maf and/or the iac and no change.

General karthief · Oct 23, 2016

Not as experienced as most on here but they need to know some basics, stock or modified, why did you put 30 pounders in it, thats like 400 hp level stuff. Dump'n the codes seems to be the first place to start, remember you should get the 11 code if stuff checks out, ask mee how I know. If you have limited experience, read the information a couple times, seems harder than it is. Don't buy into the 'you need it tuned' mentality when you have a stock setup.

FoxMustangLvr · Oct 23, 2016

karthief said:
Not as experienced as most on here but they need to know some basics, stock or modified, why did you put 30 pounders in it, thats like 400 hp level stuff. Dump'n the codes seems to be the first place to start, remember you should get the 11 code if stuff checks out, ask mee how I know. If you have limited experience, read the information a couple times, seems harder than it is. Don't buy into the 'you need it tuned' mentality when you have a stock setup.

I second this advice. Why did you feel the need to upgrade your injectors and MAF? What are your engine mods? Run codes and follow Jrichkers advice. Fuel upgrades do not add HP, they only support it. Good luck.

RockHill · Oct 23, 2016

Engine mods are heads, custom cam, BBK long tube headers, BBK off-road H, and the reason for upgrading to 30's was to get ready for future mods. I have pulled codes koeo and koer and no codes. Thanks

FoxMustangLvr · Oct 23, 2016

You could have created new problems by switching out your computer, distributor, etc. Some distributors are bad right out of the box. I'd reinstall all original parts and start problem solving.

Also, you say you have an HCI upgraded engine and you installed 30# injectors and matching MAF, and then reinstalled "stock" injectors and MAF? Why stock when you have a HCI engine? This doesn't sound right. HCI engines need at least 24# injectors and you should NOT upgrade your fuel system and drive your car BEFORE you make the performance upgrades, you do them at the same time.

FoxMustangLvr · Oct 23, 2016

RockHill said:
Engine mods are heads, custom cam, BBK long tube headers, BBK off-road H, and the reason for upgrading to 30's was to get ready for future mods. I have pulled codes koeo and koer and no codes. Thanks

No codes? As stated before if everything is ok you should get a code 11. Did you get an 11? Also do you have a custom tune for your combo or just a stock computer?

General karthief · Oct 23, 2016

So you got that 11 code right?
Hate it when I get beat to the post

Yea, what he said.

RockHill · Oct 23, 2016

No codes got the 11 code. Stock computer no tune. The reason I swapped back to stock injectors and maf was to isolate the problem. The car ran fine and ran fine when initially made the upgrade now it doesn't.

FoxMustangLvr · Oct 23, 2016

RockHill said:
No codes got the 11 code. Stock computer no tune. The reason I swapped back to stock injectors and maf was to isolate the problem. The car ran fine and ran fine when initially made the upgrade now it doesn't.

Be patient as I'm trying to get more info and understand what's going on. So before upgrading to 30# injectors and matching MAF, you were running your HCI motor on stock 19# injectors and stock MAF, right? I assume stock fuel pump too? How long did you run this combo like this? What heads do you have? It's possible when you upgraded the fuel that a new and unrelated issue presented itself.

General karthief · Oct 23, 2016

I'd verify the tps, see what voltage it starts at idle and check for a smooth sweep. Then maybe go at the dizzy if that checked out. I'm figuring the fuel pressure is good. You didn't suck somebodies cat up the intake right? Laughed my but off when a friend sucked a rag up the intake once.

FoxMustangLvr · Oct 23, 2016

Another thought is there may have been a code thrown when the issue started but you replaced that computer with another one and now the new computer hasn't realized there's a problem yet because the engine may have not run long enough.

RockHill · Oct 23, 2016

I just finished testing the tps and have no voltage signal going to the computer and no change when going through the throttle range. Going to replace that and see what happens. I've been running the stock combo since I've owned the car. The heads are pro topline that have been worked. 200 cc 2.02 1.60. With the tps failing I'll hoping that's what it is but I can't figure out why it hasn't thrown a code

FoxMustangLvr · Oct 23, 2016

RockHill said:
I just finished testing the tps and have no voltage signal going to the computer and no change when going through the throttle range. Going to replace that and see what happens. I've been running the stock combo since I've owned the car. The heads are pro topline that have been worked. 200 cc 2.02 1.60. With the tps failing I'll hoping that's what it is but I can't figure out why it hasn't thrown a code

With the new computer it may not have had time to recognize the problem. You really need fuel for that combo or you risk running it too lean in high rpms. Get a GSS340 (255lph) fuel pump to go with your new inj/maf combo. 24# injectors would be more ideal.

I hope the TPS is your problem. Good luck

RockHill · Oct 23, 2016

That's the fuel pump I'm running!!! Thanks

mikestang63 · Oct 23, 2016

You would have gotten a code for a bad TPS. Either you did the KOEO test wrong or tested the TPS wrong. DId you test the green wire for + and then the ground the DVOM to the black wire? You should be between .8 and 1.1 volts. Did you test the orange wire while grounding to the black wire? You should get around 5 volts.

RockHill · Oct 23, 2016

Had zero volts on the black wire and no change when going through the throttle range. The orange wire had 5 volts.

mikestang63 · Oct 23, 2016

RockHill said:
Had zero volts on the black wire and no change when going through the throttle range. The orange wire had 5 volts.

The black is ground- you wont get any volts there. As I stated, did you probe the green wire with the + and the ground of your DVOM to the black wire. If your TPS is bad it should have thrown off a code. Off the top of my head I think its code 63

RockHill · Oct 23, 2016

Yes I got. 96 volts

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