bad hesitation/stumble on tip-in

[kendogg]

OK, my car is having a bad hesitation/stumble on tip-in. Bone stock M20, stock chip, etc. Just put in new plugs tonight. Nothing changed. No vacuum leaks. Going to get out the DMM and my Bentley tomorrow to start checking all of my sensors. Does the Bentley give a way to check the AFM as well?? Any other idea's guys? Thanks.

[jlevie]

See http://frwilk.com/944dme/afm.htm for a way to test the AFM.

Other things that might need attention include:

1) Valve adjustment (best done every 10k)
2) Ignition wires, distributor cap, and rotor
3) ICV and correct adjustment of idle stop and TPS (and a functioning TPS)

Although you say that there are no intake leaks, that might still be a possibility and can cause this.

[kendogg]

Thanks for the link, but that seems to be specific to e cars.

Valve adjustment is ok.
wires/cap/rotor are fine
ICV is fine, shows correct ohm on my DMM per Bentley Specs.

TPS - well...Idle side of it is fine, but it doesn't see WOT. I doubt that could cause it, or could it??

Everything else tests out ok. Coolant temp sensor. AFM & IAT. No vacuum leaks. ICV passes Bentley test. This is definitely a strange one :(

[kendogg]

These were all cold tests, btw. Should I warm the car up and check the coolant temp sensor when warm? It doesn't seem to matter is the car's hot or cold when it hesitates though.

BTW - I know there are 3 coolant temp sensors. Bentley only gives specs/description of one - the middle one, with the blue plug. Wtf are the other 2? The one in the front is a single wire sensor (but looks like a 2-wire, wtf??).

[kendogg]

Also, just tested the coil.

Coil primary resistance was about .9 ohms, alot higher than the spec of .5. Secondary resistance was about 5900 ohms, a little, but not alot, higher than the spec of 5k. I'm going to test and possibly install a spare MSD coil I have and see how it runs

[kendogg]

OK, still isn't fixed.

I hear a loud-ish hissing sound from the hose going from the ICV to the manifold. So, I JB Welded that metal elbow into the TB, and the hose going from the ICV to the manifold is perfect. Is that normal to hear air hissing noise from that hose?? I put my ear right on it,a nd it sounds like it's coming from inside the hose.

Also, what should happen when I unplug the ICV? When I unplug mine, it doens't change anything.

[Kingb]

[quote=kendogg;1189005]So, I JB Welded that metal elbow into the TB, and the hose going from the ICV to the manifold is perfect. Is that normal to hear air hissing noise from that hose?? I put my ear right on it,a nd it sounds like it's coming from inside the hose. [quote]


I think that is where my little leak is comming from. I have hesitation too and have checked all the sensors also. I put teflon tape on mine but is there any other way of sealing these besides JB??

[jlevie]

From the factory the ICV and brake booster nipples are a press fit into the throttle body. With time that fit will loosen and can cause an intake leak. The easy fix is to JB Weld those fittings into the throttle body. Just be sure to throughly clean the fitting and socket with acetone first and allow 24 hours for the JB Weld to cure.

Also, what should happen when I unplug the ICV? When I unplug mine, it doens't change anything

If the TPS is working and both the TPS and throttle stop are properly adjusted, the engine rpm should rise to 900-950rpm when you unplug the ICM. That assumes that the ICV is good and not sticking, and on this car, that the Idle Control Module is good.

[peete]

Couple of stupid not so obvious things to check; dip stick all the way in?all injector harness connectors in all the way? plug wires fully seated? spark plugs all torqued?(I found this one time, embarassing) crankcase ventilation hose connected.Was it running fine before the tune up?

[AlarmedBread]

faulty impulse sensor (inductive pickup on plug wire 6) will also cause this, if not re routed properly during a tb change they can easily get cut by the waterpump.

[Kingb]

If the TPS is working and both the TPS and throttle stop are properly adjusted, the engine rpm should rise to 900-950rpm when you unplug the ICM. That assumes that the ICV is good and not sticking, and on this car, that the Idle Control Module is good.

Maybe this is a stupid question but what is the Idle control module? I only know the ICV unless its the same. If not where is it?

[kendogg]

For the hundredth time - it's not an e. There is no idle control module.

TPS seems to be working correctly, not sure about the throttle stop. Idle barely does anything when I unplug the ICV.

Peete - yes, dipstick is all the way in and seals well. Same with oil cap on the valve cover. It idles like shit as soon as I remove either, so I know thats not the issue. And no, the only reason I swapped plugs was a first attempt at curing this issue.

Kingb - and Idle Control Module is a green box in the glove box near the DME on e cars. Irrelevant on i cars.

Since we've been having this gas crisis, I've been running 2 bottles of HEET with every fillup of 87 octane. Car seems to behave much better. The hesitation is still there, but most of the power seems to have been restored.

[kendogg]

OK. Bringing this back from the dead. Problem is still there. Just did a compression test.

#1 - 180
#2 - 170
#3 - 175
#4 - 185
#5 - 175
#6 - 180

I'm stumped here guys. Please help.

[kendogg]

Also, forgot to post pics of the plugs. These have maybe 3k on them tops.