[FIXED] Vibration and sputtering while on Idle after warming up the car

Hello
This is a 2002 ford focus 2.0L Zetec SE with 383,000 Miles with (NO CHECK ENGINE CODES)
except P1000 (OBD System readiness test not complete)

Problem:

After warming up the car for 5 min I experience vibration/sputtering/shaking on idle (park mode) and upon pressing the gas pedal their is 3-5 seconds or longer delay for the RPM to go down. I have no problem driving the car but maybe on the stop light or traffic I will feel the vibration but less because it on (Drive Mode) I have done many repairs with this car and I do it myself. The problem started after doing a complete timing belt replacement and before that front and rear main seal, new valve cover gasket. Compression Test all 4 cylinders around 150-160 psi (wet and dry)

What I did to try solving the problem:

Parts
-New Motorcraft IACV from Ford
-New TPS sensor from (Autozone)
-New MAF sensor (ebay) or my original which is clean and restored
-New O2 sensor (Autozone) upstream
-New Motorcraft Ignition Coil and Cables
-New Motorcraft Spark Plugs
-New Ford EGR Valve
-New PCV and hose (O'Reilly Auto Parts)
-New Fuel Injectors

I used smoke test and found 4 vaccum leaks
-Brake Booster hose to the intake
-hose to the PCV
-Hose to fuel rail
-EGR Valve
-Clean Throttle Body (New gasket)

Observation using my scan tool (Launch CRP 429C)

IACV on first start goes 40-50% and drops to 19.92% after warm up and stays there. IACV increases to 30%+/- when Engine fan cycles and drops back to 19.92%. The symptoms with IACV plugged is Vibration, sputtering and 3-5 sec delay upon pressing the gas pedal

At IACV 19.92% I can unplug IACV harness and vibration is less. The 3-5 sec delay on the pedal before is now normal without issue.

Plugging the IACV harness back will bring all the issue again.

I performed PCM reset, IACV relearn and clear codes with NO LUCK!

I also check the IACV harness for ground and 12V voltage was (good) using Circuit tester and Multimeter

I attached some numbers from the scan tool. If you need other info from the scanner please let me know. Hope you guys could help me. This is been a headache for months but at the same time I know I'm restoring the car anyway. Thanks

What are your short and long term fuel trims at when this is happening?

Nissan Technician

At the beginning I found 4 vaccum leak and checking the (long term fuel trim) it was at 20%. Because I didn't pay attention too much I just fixed the vacuum leak immediately. Finding out the issue maybe got a little better but vibration/sputtering is still there. So now I have to start the car and check my scanner watching all the numbers in the scanner from 10-15min until I'm satisfied. LTFT now 15%+/- STFT 1.65% +/- this is while on idle for sometime. The IACV frozen@ 19.92% unless the engine fan cycles it will go up about 30% and drop back down after the cycle.
2002 Ford Focus spec says Desired RPM 700 and IACV 30%. Clearly too low! ScannerDanner's posted video he mentioned in one issue that IACV 19% is fully closed. Mine is stuck to 19.92% like its the lowest point and stays there.

Hi guys,

According to pictures, you have two diferent rpm's for the same IACV position. That means the IACV is not controling all the air passing trouhgh intake manifold. So you still have a vaccum leak.

Test: If throttle plate is completely closed, the only passage to the air enter is IACV passage. When you slowly strangle IACV passage, the engine should colapse.

I did 2 long separate smoke test which I found 4 vaccum leaks
cleaned throttle body plate and new gasket.
*What I've done similar to danner's video post regarding tampered throttle body screw by a owner.
=because I knew my IACV was too low @19.92 I had the car running in Idle while experiencing the vibration, sputtering and throttle delay 2-5 sec if I hit the gas pedal, then I unplug the harness of the IACV.
(result) no much difference. Although unplugging the IACV cures the gas pedal/throttle delay of 3-5 sec which happens when it's connected. Then I adjusted the throttle screw to match the desired RPM around 700 and reinsert the IACV harness (result) All the issue came back
=The setting that sounds good is unplug the IACV, raising the RPM between 900-1000 which I know is too high (throttle is open) and vibration/sputtering is less to none but I can't drive without the IACV.
If you think I need a a new IACV this is the second new Motorcraft IACV+ 1 aftermarket all doing the same thing.
Harness issue- I check ground and voltage all good.
PCM malfunction?
Vaccum leak I missed or any idea that I forgot to try
I have a long list of work done above. Thanks

The symptoms match a vacuum leak except for the fact that it only occurs after a warm up. That would have to be a very specific kind of leak. I have a theory that it could be related to operation of the canister purge valve. Maybe it's hanging open after being activated or there might be a leak between the valve and the canister letting it suck in unmetered air when the purge valve is activated.
I would try blocking the vacuum source to purge valve and seeing if the symptoms improve.
Hopefully you can get that idle adjustment screw back to where it belongs. That can throw a money wrench into the diagnosis.

I also cannot help but wonder about the camshaft timing since you say this happened after a timing belt replacement. If the vacuum leak testing continues to turn up nothing, I would reinspect the timing components.

Is it possible to strangle iac passage with a finger?

Due to you are having idle speed higher than desired, i am supposing you have a speed density engine.

If it's not possible to reach that passage, you can try to strangle the complete throttle body "mouth" with your hand (slowly and carefully)

Let us know your results and also baro pressure, manifold pressure, fuel trims.

I had the smoke test for a long time hoping more vacuum leak shows up but no leak from that area. I know before one hose coming from the canister had small leak but I never completly check that area. That's one thing for me to check! Timing belt... I had to redo the whole timing belt procedure 3x because of the vibration. check and double check that timing. I know its good because I never complained with the actaul driving condition. The one that bothers me is on idle at the parking lot waiting while the car vibrates and sputter.
Thanks for your suggestion Noah!

I'm in process of blocking the air passage from the IACV to see how the engine reacts. I would try your idea too. Searching for the culprit (IACV, Harness or PCM)
Thanks Guafa!

So a vibration is what your chasing?? You sure it’s not in the motor mounts?? Or does the engine actually run bad???

Engine is good and motor mounts in not that old. I got the fordpart for that. It's more like sputtering and shaking on idle (park mode)

Update!

Performed a test today

#1 Made a IACV gasket made of aluminium without holes to try to block the air passing though the IACV and still connect the harness. (result) On a cold engine I can start the car only with my foot on the gas pedal. I tried to hold the gas for 1 minute and it still stalled. Maybe if the engine is warm /operating temperature idle might hold.without my foot on the gas. The engine sounds normal but expected because the throttle is wide open.

#2 I got a Noid Light Tester and attached it to the harness and turned the key to "on"(result) No light!
Doesn't make sense... I tested the harness using my circuit tester and light went on which is ground, I used multimeter and gave me 12V

Pending! I ordered a Power Probe Circuit Tester and will check Continuity Test probably this weekend or earlier.

Anybody has a clue what might be the problem at this time? Thanks

Hi dasz,

Test #1 is telling you IACV controls idle (we already know that). This way, is not conclusive.

You should block IACV passage only at the moment engine is warm, idling, vibrating and sputtering. If engine doesn't stall, that means is getting air from another source. This is why you should reach that passage with your finger. My mistake not giving you all details of the test.

You can also try to block the complete air intake passage with your hand.

Hello guafa,

Ok I did the test again.
Started the car until operating temperature. (ford focus throttle body) Turn the car off for about 30 sec so I can pop the air intake pipe off from the throttle body and blocked the hole next to the round plate with a thick fold up shop towel (not round 2 inches openning) and immediately put the air intake back and started the car. The car started with no difference.

Did I block the correct one?
I don't expect to block anything outside the throttle body.

Has the throttle body itself been cleaned ?

Is the engine itself in good mechanical condition, is no excessive pressure in the crank case leading to excess crankcase fumes through the PCV

Andy.MacFadyen
Throttle body is clean with new gasket together with many other parts replaced. I am trying to put this car close to perfect. 383,000 miles drives very well with all 4 cylinder 150-160 psi compression test (wet and dry).
I am just seaching for the solution with this shaking and sputtering on idle after warm-up. I did not replace intake manifold gasket yet but I did a smoke test 2x and found 4 vacuum leak. So maybe I am missing something.
Thanks
See all work done from the very top

Hi dasz/guys,

I have found that method i am suggesting , is a little bit more stressing for intake gaskets, hoses and in general, little leaks than smoke test, which doesn't use any pressure.

I still believe this issue is related to a vacuum leak. Of course, until we rule it out

Dasz, please double check what i am suggesting. Engine has to be running when you block the air passage.

If you still need more details, let me know

Did you try Noahs suggest to pinch off the evap purge valve to see if it is sticking open and causing a vacuum leak. This and the hose to the brake booster can hide from smoke tests. Try pinching both of those if you haven't already.

Nissan Technician

Hello guafa,

I really had no way to block that IACV passage with my finger while its running because its inside the air intake pipe and will stall the moment i pop it open. So I had it idle until operating temperature pop the air intake and placed a fold up shop towel enough to block the passage. I placed the air intake back and started the car (result) it started fine just the same. Making sure I satisfy myself I place more shop towel around the throttle plate (result) started fine like the first time.