Need help with idle problem please

GeLsTaNg215 · Feb 24, 2006

First things first I did tons of searching and read alot of different threads including the idle surge checklist. But onto the problem, ever since I did the cobra intake and tb swap. My car dies when first started and idles really bouncy. It idles fine once the car warms up but it keeps dying until I rev it a bunch to warm it up when first turned on. So far i've tried swapping out the new tps that came with the tb for my old one and that didnt do anything. I also cleaned the iab real good also didnt work. theres no vacuum leaks anywhere I checked everywhere with carb cleaner on all hoses and gasket areas. Finally today I tried to reset the idle to see if that would help but the car wont start when the iab is disconnected, Is the iab bad? because according to the idle reset instructions you set the idle screw while the iab is unhooked but my car wont start period while disconnected. im totally lost on what else to look for, this is really getting annoying too. I dont know if this ties into the idle problem but my car seems to be running rich now too. Any suggestions would be very appreciated. :SNSign:

joel5.0 · Feb 24, 2006

Start by scanning the system for codes, do a KOEO self-test to check what other EEC-IV circuits might be out of specs. and post the codes. If the problem is that the engine doesn't stay idling when the IAC is disconnected, you may want to open the TB blade more via the the stop screw until it does.

Another alternative for the idle problem, that you may want to consider, is the installation of the IAC bypass spacer like the one shown below. LUK

HISSIN50 · Feb 24, 2006

I am with Joel - one sets the hot, no-load idle with the IAC disconnected. It should always start in that same condition. Now if the car cools off some, it might not start without you cracking the throttle open a little (if you have the IAC disabled. Otherwise the IAC should assist and you should not need to apply throttle).

It does sound like you might want to fine tune that idle reset.

Good luck.

GeLsTaNg215 · Feb 24, 2006

Ok looks like this would be a good time to buy a code reader. But as far as the iac goes, is there any way to reset the idle with how its acting now? and where could I buy that IAC bypass spacer at?

HISSIN50 · Feb 24, 2006

The dealer and resto houses sell the bypass plate. THey go for 10-20 bucks. THey dont work for more than a few guys so you can often score them cheap used.

You should be able to reset the idle as long as the car doesnt surge a bunch with the IAC disconnected (the surging absent IAC input would suggest a mechanical or tune issue).

MHO.

Good luck.

joel5.0 · Feb 24, 2006

Agree with HISSIN50, if the surge is too noticeable w/out the IAC in-line....something else might be causing it.

The spacer will only "aid" the IAC or allow a minimum airflow through the TB bypassing the IAC. Hold on to the spacer suggestion, it only works for fine adjustments, it won't solve a "gross" idle problem. LUK

GeLsTaNg215 · Feb 25, 2006

You guys are saying if the surge is too bad while the iac is disconnected then it could be something else, but the car wont even start while the iac is disconnected though. and if i disconnect the iac while the car is running the car dies. Could the iac be bad that would do that? or might be something else? I'm hopefully gonna grab a code scanner this weekend, but anymore input would be great.

HISSIN50 · Feb 25, 2006

GeLsTaNg215 said:
You guys are saying if the surge is too bad while the iac is disconnected then it could be something else, but the car wont even start while the iac is disconnected though. and if i disconnect the iac while the car is running the car dies. Could the iac be bad that would do that? or might be something else? I'm hopefully gonna grab a code scanner this weekend, but anymore input would be great.

I think we lost you. The only time the car should idle with the IAC unplugged is when the idle is already adjusted properly, and the car is hot, and there is no load on the motor. You need all 3 (esp #1).

When the motor is cold, you definately need the IAC (it functions like a cold enrichment circuit/choke on carbed stuff). And it ups the idle when you add a load (like the A/C) so you can see why we outline that the car should only idle without the IAC plugged-in, if the motor is hot and unloaded.

Me thinks you still dont have the base (hot) idle set high enough.

Though you have probably seen it, this article is helpful. I just left it at page one in case you want to skim each page to get a better idea about the dynamic at hand. The idle reset page is probably where you are actually at right now.

You asked about a bad IAC. Now, it seems to me that by our logic, your car should idle (under criteria listed above) without the IAC even present, so if it was bad, you would have cold-start and idling-with-load issues, but not unloaded, hot idle issues. Your idle is set to not need the IAC at this time. Make sense?

That's all I can think of. Good luck.

GeLsTaNg215 · Feb 27, 2006

Okay sorry for keeping this thread alive but this is getting ridiculous. My car died like 8 times on start up this afternoon and stumbles alot on take off from a stand still. Im starting to understand what you said hissin but not perfectly lol im still learning everything. So what could I do exactly to fix this problem or at least locate it. Is it possible to set the idle without disconnecting the iac? Sorry for so many questions im just trying to learn and figure this damn problem out before I go nuts. Once again I appreciate all the help so far

jrichker · Feb 27, 2006

With the engine Off, turn the idle set screw under the throttle body 3 turns. Disconnect the IAC, press the pedal 1/4 of the way down and try to start the car. If the engine will not idle, continue to tighten the idle speed set screw. Once the car starts, note the idle speed. Using the idle set screw, raise or lower the speed until you get 600 RPM +/- 25 RPM.

The engine should idle without any surging when the IAC is disconnected. If it will not, then you may have mechanical problems. Use a vacuum gauge to measure the vacuum. You should see 15"-19" of vacuum at 625-675 RPM. The vacuum gauge needle should be steady and not oscillate or flutter.

Report your findings along with the results of the computer code dump and I will try to help you.

GeLsTaNg215 · Feb 27, 2006

Okay thanks alot for that info i'll have to try that out tomorrow or sometime this week. I just went outside on my break from work and checked the tps voltage with a meter from work and it was at .89 which is kinda low so I bumped it up to right below .96 i'll see if that helped at all tonight when I leave. :SNSign:

GeLsTaNg215 · Feb 28, 2006

Just a quick update to my last post, I left work like 10mins ago and holy crap! Me changing the voltage on tps made a big difference. It didnt fix the idle problem of course but it defiantly made the car feel like it has alot more power and most important it doesnt buck under 2,000 rpms like it was.

GeLsTaNg215 · Feb 28, 2006

Alright well today I did what jrichker said to do to reset the idle and it worked as far as keeping the car alive while the iac was disconnected. But now when i start the car now the idle hangs around 1500 and then slowly drops to where it needs to be. But still bounces around between 600-800 and when I come to stop a light it hangs around 1,000 alot. I took a vacuum gauge and hooked it up the vacuum tree and it was reading between 15-20 but it kept bouncing around on the gauge too, So does this mean theres a vacuum leak?

GeLsTaNg215 · Feb 28, 2006

jrichker · Mar 1, 2006

A continously sweeping reading on a vacuum gauge means that you have an intake valve sticking open. Everytime the cylinder starts to come up on compression stroke, it blows air back into the intake manifold. That causes the vacuum to decrease and makes the gauge needle do the sweeping thing.

To locate the offending cylinder, do a cylinder balance test.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 99 for everything OK, or the number of the failing cylinder such as 22 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $33.

GeLsTaNg215 · Mar 1, 2006

Thats just depressing but then again it would make sense with all the oil im burning at heavy throttle too. I wish I had the right tools and a garage for this kind of stuff cause a shop would kill me in prices for this sort of thing to get fixed

GeLsTaNg215 · Mar 1, 2006

Well thinking about this whole situation and everything thats going on with my car does anybody know what an average rebuild would cost done by a shop?

Zero_chance · Mar 1, 2006

Youll have to figure out whats causing it to hang open. Valve spring? Guide? Bent valve? I think if the spring had broken youd definitely be having major driveability issues more than what youre saying ALTHOUGH I had a 32v Continental in my bay the other day that was driving real rough but still driving and it turned out that just the top of the valve spring broke. You dont seem to be having that kind of driveability issue though. If you have the cash or the know how you might wanna pull the heads and check the valve stem to guide clearance with a ball gauge. And then you could reseal the valve guides or have a shop do it to help in the oil burning department.

jrichker · Mar 1, 2006

The sweeping reading may be something as simple as a valve adjusted too tight, or not enough shims under a rocker. Do the cylinder balance test first to determine if you have a weak cylinder and go from there.

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