Idle surges then engine dies

[795.0pacecar]

First and formost I have tried almost all of the remedies on the checklist.

I have tried 2 new IAC valves, 2 new TPS sensors and I have adjusted them with no good results. I have made sure all my grounds are good, I also added new grounds. The O2s have about 20,000 miles on them. The ECT and ACT sensors are new and the PCV is new. I have played with the 10 pin connectors and that didn't do anything. The computer doesn't throw any significant codes. I also havn't been able to find any vacuum leaks.

The idle will surge from around 500rpms to 1200 then level out, or die depending on its mood lol. It seems that it idles worse when there is any kind of significant electrical load. When the fan is on it doesn't idle great, and it idles especially bad when the A/C is on. This is kind of wierd to me because I have a 3G alternator.

Any insight is greatly appriciated, this whole ordeal is making me start to consider converting back to carb.

 

[TUFFGT]

Do you have a mass air meter? I notice you said you are using the efi of an 88 mustang. Those are speed density computers and may act funny with modded motors. If you do not have a mass air meter this might be a problem with the mods you have in your car.

 

[795.0pacecar]

Yeah its still SD. I dont realy want to go to mass air, but I will if I have to. I was under the impression that as long as I have sufficient vacuum Sd would be fine with my mods.

 

[PoopDawg]

Grounds. Atleast a 4 gauge wire from the battery and a 4 gauge from the engine to the chassis... easy to do from the block to the sway bar mount. This will probably fix the problem for about 10 bucks.

 

[795.0pacecar]

Grounds. Atleast a 4 gauge wire from the battery and a 4 gauge from the engine to the chassis... easy to do from the block to the sway bar mount. This will probably fix the problem for about 10 bucks.

I have a 2 gauge going from the battery to the block, 2 gauge from the same bolt on the block going to the chassis, 4 gauge going from the battery to the chassis.

 

[HISSIN50]

The initial thought I had was about the IAC (a load seems to cause issues). If an aftermarket IAC(sounds like it), did you set the idle with it connected? And did the unit need to be mounted upside down (some do)?

Good luck.

 

[795.0pacecar]

I set the idle with the IAC unplugged. I cant mount the IAC upside down, the tube that goes to the valve cover filler neck blocks it.

 

[HISSIN50]

If the IAC was of the flavor that was needing to be mounted upside down per design/instructions, it wont care why it cant be mounted properly. If it is a brand which does not require being mounted upside down, then no worries.................

Seems to me that SD cars have the idle set with the IAC connected.

Good luck.

 

[795.0pacecar]

Its wierd, it seems to idle ok as long as there isn't any substantial engine or electrical load. I think its mostly the engine load when the compressor comes on thats making the idle surge. The computer is in no way conected to the compressor so it doesn't know its supposed to adjust the idle up for it. The thing is before I did any engine mods this worked fine, the engine would still adjust its idle when the compressor kicked on.

Im seriously considering going to mass air when I have the money for it. I already have the correct wireing harness, all I need is an A9P comp and a MAF sensor.

 

[HISSIN50]

The computer is in no way conected to the compressor so it doesn't know its supposed to adjust the idle up for it. The thing is before I did any engine mods this worked fine, the engine would still adjust its idle when the compressor kicked on.

In stock form, this is untrue. I thought you might have rewired things during the transplant, but you mentioned that it used to compensate for the load of A/C.

The computer does know that the A/C is on and kicks the idle up, and the IAC is what facilitates this increased idle.

I'm confused about what is going on, so I'm just stating information (take no offense). ............

Good luck.

 

[795.0pacecar]

I know, in stock form thats untrue, but Its something I did to make the swap easier on myself. Without the compressor on and the fan on low speed it idles fairly steady around 700-750 rpms, and occasionaly bumps up to 900-1000. With the compressor on and the fan on high speed the idle surges from 550rpms to 1300 and occasionally will level out around 900rpms. Theres no rhyme or reason to it, it just does it whenever, but ever since I adjusted the idle with the IAC unplugged it has had a more acceptable idle.

 

[HISSIN50]

I understand your situation now.
But because I havent run a 5.0 like that, I cant offer any great ideas.

You have the idle set about where I would. If you bump it up more for when the A/C and E-fan are on (raising the idle to maybe ditch the surge), the idle will be too high with no A/C on (I surmise).

If the issue only gets real bad when the A/C and fan are on, it almost makes someone wanna swap back to a mechanical fan...........

Hey, I wonder if one of Baskin's controllers would help bandaid the problem. Or figure a way to get the puter back in the loop with idle compensation........... (just thinking aloud with you).

Good luck and bump off page 2.

 

[795.0pacecar]

I was thinking about getting the DCController when I have the money for it. I want to ditch the spal controller, it worked good for maybe a month, but it sucks now, it likes to turn on high speed when low speed is supposed to be on, no matter how many times I set the temp. as long as the A/C compressor is off the fan has no effect on the idle at this point.

I dont think the fan is the problem, it idled like crap with the mechanical fan, although I never tried it with the A/C. I'll just keep playing with it and start saving up for a mass air conversion. I've been putting it off because I wanted to be one of the few who have a pretty stout speed density controlled engine, but now I just dont care anymore. I just want it to run right.

 

[PonyBoy90]

Maybe your MAF is messed up?

You running a K&N filter in that car? I know the filter oil is known to gum up the sensitive MAF wire sensors.

I'll be taking apart my air-inlet tub this weekend and cleaning mine out with some electric cleaner and a Q-tip.

 

[795.0pacecar]

Maybe your MAF is messed up?

You running a K&N filter in that car? I know the filter oil is known to gum up the sensitive MAF wire sensors.

I'll be taking apart my air-inlet tub this weekend and cleaning mine out with some electric cleaner and a Q-tip.

Speed density. No mass air meter.

 

[stangGT87]

My 87 would do the same thing... it would idle fine when just sitting there but when i turned on the lights it would start surging....the problem was a bad vacume line... after 35 cents at autozone it was all better. Have you checked all the vacume lines?

 

[795.0pacecar]

My 87 would do the same thing... it would idle fine when just sitting there but when i turned on the lights it would start surging....the problem was a bad vacume line... after 35 cents at autozone it was all better. Have you checked all the vacume lines?

I have checked as many as I could see. Most of them are new, the only ones that kind of worry me are the brittle plastic ones, but Im pretty sure they are alright. The car is idling ok right now, although it idles alittle high.

 

[tddpop]

I know you said you checked for vacuum leaks, but to me it sounds like that is most likely the culprit, that or a electrical problem. I would check all TB, intake manifold gaskets, and any that could cause vacuum leaks, as well as all vacuum line connections throughout the engine bay. EFI swaps into older cars can easily break vacuum trees and crack lines, and cause wiring problems. I would go through all the vacuum connections, pertinent wiring connections, and all gaskets. It's a lot of work , I know. No offense in suggesting something you already did, just trying to go through it in my head. It may be you need a new battery or alternator as well. Most major parts stores will check them for free. Hope my meager knowledge has helped any.

 

[795.0pacecar]

The engine ran perfect before the heads and intake. So Im not worried about any vacuum lines anywhere but around the engine like manifold vacuum lines, but I replaced all of them when I put the new intake on. I've also sprayed carb cleaner around the intake gaskets and I didn't hear any change in engine RPMs.

I think I either have the idle set wrong, or I need to convert to mass air, or even both. I think that the speed density computer tries compensate for the added airflow at idle but it cant, so it surges.

 

[tddpop]

The engine ran perfect before the heads and intake. So Im not worried about any vacuum lines anywhere but around the engine like manifold vacuum lines, but I replaced all of them when I put the new intake on. I've also sprayed carb cleaner around the intake gaskets and I didn't hear any change in engine RPMs.

I think I either have the idle set wrong, or I need to convert to mass air, or even both. I think that the speed density computer tries compensate for the added airflow at idle but it cant, so it surges.

Sorry, I never took the time to read your mods. You probably do need to convert to mass air, those computers are very picky. In the mean time you could try and mess with the idle to see if it helps.