91 Fox cold start problem

[wakarimasen]

Hi. I've got a 91 Fox (digifant injection) that annoyingly runs very rough when starting cold at idle, almost stalling... especially first thing in the morning. If I try to drive it in this state, it will barely chug along, so I've got to sit there for a good few minutes with my foot on the gas until it warms up enough and begins to run properly. It also does this later in the afternoon when I leave work and it's been parked all day, but is noticably not as much of a problem.

Once it's warmed up after a few minutes and I can drive it, i have no further problems... no hesitation or anything.

I've replaced the coolant temperature sensor suspecting that was it, but to no avail. My hunch is that it's not running a rich enough mixture when cold starting, but that's just my guess. Any suggestions would very very much be appriciated! Thanks.

[mdwelsh]

Originally Posted by wakarimasen

Hi. I've got a 91 Fox (digifant injection) that annoyingly runs very rough when starting cold at idle, almost stalling... especially first thing in the morning. If I try to drive it in this state, it will barely chug along, so I've got to sit there for a good few minutes with my foot on the gas until it warms up enough and begins to run properly. It also does this later in the afternoon when I leave work and it's been parked all day, but is noticably not as much of a problem.

Once it's warmed up after a few minutes and I can drive it, i have no further problems... no hesitation or anything.

I've replaced the coolant temperature sensor suspecting that was it, but to no avail. My hunch is that it's not running a rich enough mixture when cold starting, but that's just my guess. Any suggestions would very very much be appriciated! Thanks.

My first question would be where do you live. I am seeking ambient temperatures. Does this occur whether it be Winter, Spring, Summer or Fall?

Secondly, with a Digifant I(California only) or II(I am only familiar with The Digifant I) there is an OBD(on board diagnostics) system and does your orange "check" engine light immediately turn off after starting(VERY IMPORTANT INFORMATION) or does it either stay on for a brief period then turn off and then later while driving come on again?

First answer these questions and then we can proceed.

You may e-mail me at: mdwelsh@peoplepc.com

Mark

[wakarimasen]

I live on the west coast of Canada. My problem is at it's worst when it is early in the morning, around 8am... The temperature outside this time of year, at this time of the morning, is in the mid 40s to low 50s (8-12C) with humidty around 80-90% (in case that helps). It takes about 2-3 minutes of warming it up... usually the temp needle's got to get just to the first white part of the guage. In the afternoon, when the outside temperature is around 80, the problem is gone after less than a minute. I've had my car in storage for about 6 months, had been driving it again for about a month, and then it seems this issue just occured.

I've had no occurance of the check engine light. Also, it's a Digifant II, so i guess that means that it's not possible to have a diagnostics check on it. Is this correct?

Thanks for your reply.

[mdwelsh]

Originally Posted by wakarimasen

I live on the west coast of Canada. My problem is at it's worst when it is early in the morning, around 8am... The temperature outside this time of year, at this time of the morning, is in the mid 40s to low 50s (8-12C) with humidty around 80-90% (in case that helps). It takes about 2-3 minutes of warming it up... usually the temp needle's got to get just to the first white part of the guage. In the afternoon, when the outside temperature is around 80, the problem is gone after less than a minute. I've had my car in storage for about 6 months, had been driving it again for about a month, and then it seems this issue just occured.

I've had no occurance of the check engine light. Also, it's a Digifant II, so i guess that means that it's not possible to have a diagnostics check on it. Is this correct?

Thanks for your reply.

I am doing some research from the Bentley Manual and you are correct in that the Digifant II does not have an OBD similiar to the Digifant I. However, there is an instrument that VW mechanics use but are not available to the public and besides they are very expensive. Please do not wast your money just yet.

What I did discover is the following information from the Bentley Manual.

Symptom: Rough idle, stalling(engine cold).

Probable Cause:

A)Coolant temperature sensor faulty.
I believe that you have replaced this. Diagram 7.3

B)Auxiliary air regulator faulty.
Inspect and clean or replace as necessary.

C)Intake air preheating system faulty.
Test intake air preheating system and replace faulty components as
necessary. Diagram 7.2

D)Intake air(vacuum leak).
Checkfor loose oil fill cap or dip stick. Inspect intake air conponents
for leaking hoses, hose connections, and cracks or other leaks.
Repair as necessary.

E)Oxygen sensor heating too slowy.
Test oxygen sensor heater circuit. Diagrams 7.7 and 7.8
Also see EXHAUST SYSTEM AND EMISSION CONTROLS.

F)Electronic control unit faulty.
Make electrical tests at control unit connector. Replace faulty control
unit. Diagrams 7.7 and 8.7.

This is quoted from the Bentley Manual(section 5, pages 48-49). The diagrams begin on page 51.

I do not know but it very well may be the oxygen sensor. Unplug it and start the engine and drive the car for a short distance. If there is improvement this is a good place to start. DO NOT leave the oxygen sensor disconnected too long as this could damage the system. If this is the problem you can find them online for $50 to $150 so let me know if the problem is the oxygen sensor and I will search for the cheapest. Mine is a three-wire sensor so check how many wires are on yours.

I do not have the hardware to take pictures to send to you so perhaps you may find a Bentley Manual at the library reference desk. There is also another manual called Mitchell and you can download and print anything that you want. You can do this! Just take your time and try the library.

If you plan on keeping the vehicle then procuring a Bentley Manual is a good investment and you can purchase a new manual for $25 from Amazon.com. Perhaps a used manual for $15.

To be redundant, it does sound that it very well may be the oxygen sensor.

Good luck and feel free to contact me for any information from the Bentley!

Mark

[wakarimasen]

OK, I just recieved my Bently manual and will be troubleshooting this problem. I will keep you posted. Thanks for your help thus far.