Cold Start Issue.....bogs down just touching throttle

[tom04841]

If my engine isn't up to operating temp, any time i try to take off, or after shifts, the car bogs down pretty bad. It bogs for a second or two, then comes out if it. When this happens, I have noticed on my wideband that my afr jumps to @ 20:1 then falls back to @15:1.

I have ran multiple boost leak checks....none.

Checked base timing....good

EGR is blocked

My profile is updated!

Anyone have any ideas what my problem is?

[zippyshoe]

A couple of possibilities that come to mind:

1. Faulty coolant temperature sensor - Using your logger, monitor the coolant temperature sensor on a cold start.

2. Faulty Idle Speed Control (ISC) motor.

Also, how does your fuel pressure look when this bogging occurs?

[tom04841]

Originally Posted by zippyshoe

A couple of possibilities that come to mind:

1. Faulty coolant temperature sensor - Using your logger, monitor the coolant temperature sensor on a cold start.

2. Faulty Idle Speed Control (ISC) motor.

Also, how does your fuel pressure look when this bogging occurs?

Coolant temp sensor climbs steady on logger....which kind of rules that out.

I have a spare ISC that checks out ok. I will throw it on and see if it changes.

Its hard to monitor my fuel pressure....it is mounted right to the AFPR. I guess tomorrow morning i could start it, then feather the throttle from under the hood.

Once i get these couple things done, i will post back.

[CanadianTSi]

I just noticed the Exact same thing happening to my car this morning, it started after I added 880's and an Aeromotive AFPR.

[zippyshoe]

Originally Posted by tom04841

Coolant temp sensor climbs steady on logger....which kind of rules that out.

I have a spare ISC that checks out ok. I will throw it on and see if it changes.

Its hard to monitor my fuel pressure....it is mounted right to the AFPR. I guess tomorrow morning i could start it, then feather the throttle from under the hood.

Once i get these couple things done, i will post back.

Replacing the ISC with a known-good ISC sounds like a good idea - this seems to be one of the most common causes for a poor idle. As far as checking your fuel pressure, you could probably just check your base fuel pressure by momentarily disconnecting the vacuum hose from the AFPR (43.5 psi). Then, re-connect your vacuum line and see what your fuel pressure is at idle (around 34 psi, depending on your vacuum at idle). One more item to check - if you have had your timing belt replaced recently, you may want to check that the timing marks on your camshaft sprockets line-up correctly with cylinder #1 at TDC. If either sprocket is off by even a single tooth, this will cause a rough idle.

EDIT: I see you have a 1G - your base fuel pressure should be around 37 psi rather than 43.5 psi.

[tom04841]

Originally Posted by zippyshoe

Replacing the ISC with a known-good ISC sounds like a good idea - this seems to be one of the most common causes for a poor idle. As far as checking your fuel pressure, you could probably just check your base fuel pressure by momentarily disconnecting the vacuum hose from the AFPR (43.5 psi). Then, re-connect your vacuum line and see what your fuel pressure is at idle (around 34 psi, depending on your vacuum at idle). One more item to check - if you have had your timing belt replaced recently, you may want to check that the timing marks on your camshaft sprockets line-up correctly with cylinder #1 at TDC. If either sprocket is off by even a single tooth, this will cause a rough idle.

EDIT: I see you have a 1G - your base fuel pressure should be around 37 psi rather than 43.5 psi.

My idle is fine.....it is just when i touch the throttle when the motor is cold that it bogs down. If i don't touch the gas, it idles fine. Once warm the problem doesn't exist.

Base pressure is at 37.

I just rebuilt the motor....all timing marks were triple checked before installing, then checked again about 200 miles ago......after the problem started.

[zippyshoe]

Well, maybe replacing the ISC will yield some positive results.

[scottsee]

Sounds like the TPS isn't alligned properly in the TB, and when you tap your throttle the ISC is not switching off. Pretty common..

[tom04841]

Originally Posted by scottsee

Sounds like the TPS isn't alligned properly in the TB, and when you tap your throttle the ISC is not switching off. Pretty common..

But only when cold? i will check it out anyway.

[jongreene]

My car had similar symptoms when the ecu was on its way out.
The bogging was more like it was only running on 2 cylinders.....