1990 8v question

[kubik1981]

YEsturday i had a problem the splined rod on my clutch pedal broke in half. I found one and installed it today. well i unhooked my battery and had to unplug my computer to get the old clutch ped. out and the new one in. WELL now when it warms up and idles it jumps from 800 to about 1500 rpms and back down to 800. any ideas. also when i went to remove the blue connector from the computer it was never locked in the computer.

[JamesG]

You didn't disconnect anything else?

Do an ECU reset (pull the "radio and dome light" fuse), and see if that helps?

[kubik1981]

no i did not unplug anything else. But the idle does not surge anymore, now it just idles at 1500 rmps when warm. I have had nothing but problems since i had the motor installed at a small local garage. Now i got everything running good except the idle problem.

[jtgh]

and that ones the tough one.
Idle can be high for 2 reasons:

1: AIR leaking into the induction plenum (intake man) ( 8Valve only)
2: idle is not set correctly , (long procedure for that in the FSM including setting the duty cycle , do not turn the bottom screw on the TB at the throttle bell crank.
it is factory set . There is a procedure if you want it just ask.

but first find all air leaks,
sounds hard ( it can be if intake gasket leaks but most likely not )
pinch all vacuum hoses (many ) [not IAC top hose or PCV hose) and listen for RPM drop
if you hear a drop then that hose is leaking,
always pinch close to plenum side.
that trick works on most any car.

get some needle nose pliers and pinchaway.


The IAC top hose always sucks clean air to set you idle speed.
The PCV alwasy sucks becuase is it keeping the crank case gases from polluting the world.

Make sure some dweeb, didnt put in a PCV valve off a mac truck,
that would be bad, get the correct valve for THIS car, it is calibrated for 1.6L .

thats a start and thanks or saying 8V !!!

[kubik1981]

all vacuum lines are new and the pcv valve is new i just put a new one in about a month ago. So i guess if you could send me the procedure on adjustiung the idle it would be appreciated, Also your welcome on the 8v comment.

Originally Posted by jtgh

and that ones the tough one.
Idle can be high for 2 reasons:

1: AIR leaking into the induction plenum (intake man) ( 8Valve only)
2: idle is not set correctly , (long procedure for that in the FSM including setting the duty cycle , do not turn the bottom screw on the TB at the throttle bell crank.
it is factory set . There is a procedure if you want it just ask.

but first find all air leaks,
sounds hard ( it can be if intake gasket leaks but most likely not )
pinch all vacuum hoses (many ) [not IAC top hose or PCV hose) and listen for RPM drop
if you hear a drop then that hose is leaking,
always pinch close to plenum side.
that trick works on most any car.

get some needle nose pliers and pinchaway.


The IAC top hose always sucks clean air to set you idle speed.
The PCV alwasy sucks becuase is it keeping the crank case gases from polluting the world.

Make sure some dweeb, didnt put in a PCV valve off a mac truck,
that would be bad, get the correct valve for THIS car, it is calibrated for 1.6L .

thats a start and thanks or saying 8V !!!

[jtgh]

but, did you pinch the hose, not just hose go bad, its those other things,
mine had them ALL.

the diaphrams cracked will leak , they must be tested .
the pinch test is for those people with out the Mityvac or HF cheap version.
pinching discovers 2 faults per pinch, see?

just a simple pinch.

next is bad EGR gasket ( or leaking EGR)
then the gasket under the iAC missing or cracked.

keep an open mind about leaks,

if the RPM drops , the hose or the diaphraphm is bad.
EGR diagphram, , HIgh Idle Dashpot diagphram, , the brake booster diaphragm can leak like crazy. Pinch that huge hose and listen.

is your idle vacuum 19 inches HG.

the 16 ways of racing . (fast idle)
click>>>racings

if all leaks are tight.

then (idle path normal)
fresh-air

the idle procedure is on the above page , i have the FSM pages I can send you. ( this is my condensed version)
you have to place a jumper and check the duty cycle on the IAC valve.

5 paths and very tricky this TBI is.

[kubik1981]

ok i will try the pinch test is it best to do warm

[kubik1981]

i don't know what i was thinking but before the clutch pedal problem the truck did idle at 800 when warm. Now does that make any sense

[jtgh]

clutch and idle are independant unless clutch is dragging.

On the 8v engine it is called a speed density system.
this system is completely different than the 16v system.

Our 8v , automatically always mixes perfect fuel quanties to the engine based on actual air flowing in to the engine. (MAP sensor)
due that fact , RPM is dependant on only 3 things.
1: any leaks ( all leaks on 8v cause high idle )
2: any of the 5 normal idle source paths on the TB.
3: ECU can drop to a mode called Limphome and this drops the idle
adjustments software , result is unregulated idle.

if false air leaks can not be stopped the ECU can not control idle becauseon 1 simple fact , the ECU shuts off the IAC and the idle is too fast and the ECU just plane gives up.

it is like 2 faucets filling a sink, and yours you shut off to be surprised that false faucet is filling away to over flow.
hope tha make since.

[jtgh]

engine swap,?
make sure that Dashpot circuit is working.
the dashpot opens the idle at first start, (via a spring)
next as engine revs real high ecu counts 200 turns of crank or a time count of 5-10seconds (i dont know for sure) then the ecu commands open the DASHPOT vsv valve, this immediately drops
the idle to 800 to 1200 depending on coolant temperature.
spec is 1200, then it drops as the lower IAC (thermo type) drops th rpm down to 800 and then the top IAC takes over idle control.
all these things must work perfect to get to that end point.

look at dash pot , is it retracting ( letting go of throttle).?
no ,then it is busted.