Idle issues with my 96 cobra

[TheMarkness]

Hey guys I'm Mark and I'm new to these forums and to well the Cobra and the DOHC motor, and well on top of that Superchargers so what an adventure I'm in store for :rolling:

Well the issue I'm having and plagued me on the way home from picking this car up (5 hours away) is that for one it doesn't want to idle, It will sometimes but other times it'll flat out just crank and die, crank and die, crank give it some gas and it'll idle up a little high and usually drop and hold about 900-1000 rpm.

The bigger issue is that everytime I clutch to change gears or to go neutral to a stop it hangs at roughly 1900-2000rpms and will hang until i come to a complete stop which after about 4-5 seconds it will come down to about 900-1000rpm roughly. Again this is with car in neutral; it has to be at a dead stop or they'll continue to hang (no foot on gas either).

I've read up on this lovely form beer, and went through countless google search's to come up with the IAC as a culprit of sticking rpm's and idleing issues as I've explained. The unit's only 6 months old so It's hard to put fault there but I went ahead and removed it (looked clean and new), cleaned it and shook it up with cleaner in it and then dried and re-installed. Pretty much the same issue still. I notice if I run the A/C it does help the idle from dying so bad (guessing extra load on the motor).

The car has been tuned for all the changes including BBK longtube headers and the Vortech V-1 S trim kit. Driving wise it runs great just it won't idle for anything and the rpm's stick. Checked the throttle cable and it doesn't seem to stick at all seemed free and didn't look out of place.

I've heard other mention checking the TPS sensor for a certain voltage range and to use it to dial in the idle with the adjustment screw (not sure where it's located or whats the process to check). It's the factory throttle body to my knowledge (Ford markings on it).

I'm excited to own a well maintained Cobra with tasteful work done to it. The guy I got it off of is nice enough to pay for parts if I need to replace something! Alas I'm sure everyone here is sharper then the guys at the LS1tech forums right :-D

Motor specs as I know if that helps:

Steel crank
Manly rods with ARP bolts
Forged pistons
ARP hardware
Sean Hyland cams
Vortech S trim Kit (V-1)
42lb injectors Motorsport
80mm MAF
adjustable fuel reg.
new coil packs both
new TPS sensor (6 months old roughly)
new IAC motor (6 months old roughly)

Thanks again guys!

 

[Tabres]

If I were you I'd be setting the voltage on the TPS.

Just because the part is new doesn't mean it can't fail. I chased a problem all damn summer that turned out to be my brand new and perfectly set TPS decided to die and was giving me all sorts of goofy readings and playing hell with the car.

I still, like you, have a little bit of a hanging idle but mine is nowhere near as bad as yours. I'm just going to ride it out until the end of the season and have the car tuned next spring to take care of it.

 

[TheMarkness]

How do you exactly check the voltage on the TPS or adjust the idle for that matter. I'm not sure where to exactly begin though I can figure it out quickly I'm sure with a little guidance.

Also inside the IAC; the little black plastic looking valve piece should I be able to freely move that with my hand or should it be pretty stiff when out of the car?

Thanks again everyone!

 

[Tabres]

Get a volt-meter and probe the middle wire on the TPS. With the key in the on position but the car not running the TPS should be set ideally at .97 volts. If not, back the screws off that hold it in place and you can roatate the body of the TPS until the desired setting is achieved and then retighten it.

 

[MKSVT]

i just installed an accufab and keeping getting a code for tps voltage low input, I installed a new tps when i put the accufab on. I tryed checking the voltage with the method listed above and i get nothing, Could this indicate that its bad.

 

[RubberDown]

yeah, you should hit the middle pin on the plug with the positive and the ground to the negative on the battery and come up with something. If you arent, there is something wrong with the tps and you need a new one.

 

[98 svt]

Also inside the IAC; the little black plastic looking valve piece should I be able to freely move that with my hand or should it be pretty stiff when out of the car?

The black plunger looking piece should be rather stiff if you try to move it.

 

[venom1997]

it is a good posibility it is your tps but i had the same excact problem and turns out it was in my old tune so when i got the car retuned at a different tuner problem was solved i have diablosport cmr chip what is your tune

 

[TheMarkness]

Moved the TPS sensor but even when loose i could only adjust about between 1.05-1.12 or so, it didn't have alot of moving room. Do I need to adjust the actual throttle plate/butterfly valve; If so where would that be located.

Thanks again guys.

 

[Tabres]

From my experience, adjusting the stop screw will cause you nothing but grief in the long run.

Is it the stock throttle body? I would honestly just replace the TPS. They're not that expensive.

 

[TheMarkness]

Alright a little update guys.

First off I went ahead and replaced the IAC with a brand new motorcraft part from Ford with new gasket,

Next got the TPS sensor removed, enlarged the screw holes to give me better adjustment room as I read some come with more space in the holes for adjusting when installing.

After enlarging the holes I reinstalled it and got it right on .97 volts with ease; tightened down and gave it a test drive. Still having the same RPM hang issue. I notice it's like a setting/computer is sticking because it's not physically the cable. I can rev it to 3000rpm and it'll then stick to 2900rpm or so until I completely stop and then after about 5 seconds it will again drop to 900-1000rpm for idle. Driving around 2000+rpm put in the clutch go neutral and release cluth and hangs ti'll a complete stop. Like I said rev it at that time and it sticks up higher until a complete stop.

The TPS is about 6 months old and it is adjusted to the right setting. We checked voltage with the pedal to the floor and read about 4.52 or 4.55 can't remember and of course double checked again after a test drive it was still .97

Anything else I could be missing. MAF maybe dirty or need cleaned; would it cause RPM stick. VSS sensor on the tranmission cause that, don't know how it would stick in neutral without clutch or tranmissiong engaged. Just shooting at anything I can think of.

Thanks again guys!

Oh yeah I forgot to mention got a fresh oil change today also.

-Venom1997- Have no clue on my tune, guy had it tunned for the parts on it and had a stock tune chip still also, no clue exactly what all was tuned but he seems to have had the issue before maybe not sure if it was to the same degree. It drives fine but clutching and sticking rpm's at 2000+ is terrible and unacceptable; not to mention killer on gas.

 

[venom1997]

tune mabey:shrug: thats what mine ended up being

 

[98 svt]

Is the IAC broken? From the question you asked, it sounds like it.

 

[TheMarkness]

Replaced IAC with a brand new one from Ford which made no differnce. The one I removed looked brand new and seemed okay to me (about 3 months old). Anything I could be missing before I try going to find someone who can tune in this area?

The factory air temp sensor is dangling in the fenderwell not hooked up don't know if that could cause something.

Also sounds like my electric air pump also in the same passenger fenderwell is kind of loud and gets really warm like it's warn out.

And I'm thinking maybe the MAF could need cleaning. I'm just trying to see if somebody has something else I might have missed .

Thanks guys!

 

[TheMarkness]

Update guys may be on the right path:

Just digging around cleaning the MAF last night and also cleaning any other electric connectors to sensors and the IAC I noticed that there was a vacuum line off the blow-off valve routed kind of funny down low on the motor traced it and it was just hanging under the car.

I'm assuming that's supposed to be routed and plugged into the engine vacuum somewhere :beer:; Now I looked at the T up on the motor and it's completely full so I'll have to dig around the motor unless it was never plugged up in the first place.

Let me know your thoughts guys maybe this is what it's been all along epper:

 

[9cobrastang7]

I was about to post up and tell you to check your vacuum lines. This could most certainly be the culprit of your hanging idle. I have my BOV tapped into the back passenger side of the intake hat maybe try searching around there for where the BOV vacuum line goes.

 

[TheMarkness]

Looked back on the back of the passenger side of the intake and saw a T connector with vacuum coming from the manifold into the T which gave vacuum to a canister on the intake and to some cable running down the passenger side fender area.

I put a Y fitting on the vacuum from the manifold to give the BOV a line and the T connector a line which didn't really help much. Feels like it revs a little better but not much else going on still hanging/sticking idle at 2000rpm until a complete stop.

I noticed again that now sometimes when I go to start the car up it won't idle and just die until I've gotten in gear and moving then it will idle again.

Some people have mentioned EGR valve sticking as a possibility what do you guys think about that? What is on the coming from the IAC to the duct before the TB. Looks like it has a little plastic box in the middle of the tube anything to look at there?

Thanks again everyone I will figure this out :rockon:

 

[9cobrastang7]

Do you have a boost/vacuum guage? Do you have stock cams? Did you find where the vacuum line originally came from before it was disconnected? I know you said you put in a Y-split but there has to be an original T-connector where it was hooked up before. How long was the BOV vacuum line diconnected? I hope you weren't into boost much of you may have F'd up your compressor blade on your supercharger!

 

[TheMarkness]

Yes I have a vacuum boost gauge, Sean Hyland cams, forged this and that. There is no other spot for a vacuum line anywhere that it came from, I looked the whole engine bay over looks like someone started unhooking and plugging for whatever reason. I noticed that the hose connected on the passenger valve cover was laying by the inner fenderwell on the opposite end. I read up on the forum some and it looks like it's supposed to be feed back into the cold air intake ( tube before the throttle body, which was plugged before) since it's part of the PCV system. After doing that the car seemed to run about the same/ little better coming down on RPM's with the vacuum line hooked up and the hose hooked up.

I haven't been in boost at all really, I noticed since hooking things up right for the first time I've gotten into boost a hair (just normal driving and down shifting a little), though now it looks like i blew my oil cap which was actually a ford racing air breather that was rubber and shoved down in the oil cap hole. Guess it couldn't handle the correct pressure? Blew oil everywhere and scarred me thinking I did something horribly bad. I didn't hit but 4psi or so.

I went to autozone and got the correct oil cap to go there that screws in and has a rubber gasket on the top to seal to the valve cover. I since unhooked the hose from the cold air intake and put the vacuum plug back on for now.

The vacuum line to my knowledge has been unhooked since I got the car on the blow off valve.

So the PCV system is okay on this car right for a supercharger application. PCV from driver side valve cover to hose/plastic/hose to intake driver side; then hose from passenger side valve cover to cold air intake. Let me know if that is not right please!

Thanks!

 

[9cobrastang7]

Well the vacuum might be different than normal because you have different cams but it should be somewhere around 21/hg around idle. If you have a vacuum leak it should be much less than this which will cause a hanging idle.

As for the PCV... the passenger side needs to be before the compressor blade! This is very important. It needs to be on the pipe where the filter is. If it is after the compressor you will be compressing your crank case pressure which is very bad!!!!! As for the driver's side there should be a plastic pcv valve which should then connect to a rubber tube no more than 6 inches long to the top of the intake hat (there should be a bard that sticks out)

As for the idle air controller it should be connected right before the throttle blade. It should be running right infront of the intake assembly over the alternator.

One more thing is that I don't completely agree with crank case breathers. I prefer the pcv setup that I have mentioned above which is how Hellion power systems instructed me to set it up and I trust them over any other person to tell me otherwise.

Edit: It sounds like your supercharger should be alright. Just make sure to hook up your BOV before getting into boost again!