Re: '87 5KTQ performance trouble

[DeWitt Harrison <de@aztek-eng.com>]

On Sat, 24 Jan 1998 16:18:07 -0600, ColinHames wrote:
>[ ... ]
>        My first problem is the car starts to stumble about a minute
>after a
>cold start.  This continues until it is fully warmed up.  Even after is
>warms up there is very mild surging at partial throttle.  I have tried a
>warm regulator from '88 5KT that is running fine and that didn't help.

My SWAG is a broken/intermittent intake air temperature sensor (located
at the IC outlet). The ECU will back off the boost and if it thinks the incoming
air is too hot. The Bentley calls out the correct resistance. If the sensor
is intermittent, the ECU can do other silly things. There is also an error
code for this sensor. Do you ever get an engine check light
blink while stumbling/surging. Try to reproduce the surging without
putting your whole foot in it and then pull the codes.

>        Second,  the car very rarely  exceeds 1.2 bar of boost.  Once in
>a
>while it seems to run great (1.4 bar I think is normal) only to return
>to it's pokey state after a couple miles or after restarting the car.

It's hard to pin down "normal" since the gauge is inaccurate by design.
My stock ECU used to show 1.2 to 1.3.

>The throttle switch and ECU have been replaced and also various breather
>hoses so there shouldn't be any vacuum problems.
>        Occasionally the check engine code 2141 for knock sensing comes
>on.

DeWitt Harrison   de@aztek-eng.com
Boulder, CO
88 5kcstq