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Cold start/idle Issue! - Printable Version

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Cold start/idle Issue! - tquick79 - 04-22-2019

Hello ! I’ve got an issue with my 89 sidekick, I’m about to pull my hair out trying to find a problem with starting and idleing when cold.. It will start eventually after cranking off and on for 45 seconds or so but then it won’t idle real great at first until it’s ran for a minute or so. Once the idle does finally come up it will only drop to about 1100 rpm after it’s good and warm. Here’s what I’ve done so far,,, new timing belt, new crank sprocket, new timing belt tensioner kit,, new water pump, new heater core. Tested the ECT and IAT and both appear to be in working order according to the resistance chart. New fuel pump, filter and pressure regulator.. I disassembled the throttle body cleaned and inspected and reassembled with new gaskets and o rings. When I had the throttle body apart I inspected the IAC valve and it appears to be working. I recently put a timing light on it and the timing was off so I set the timing right at 8 degrees and that did help a lot and it does start better but it should start right up and idle good without having to feather the throttle at all. The only thing I’m unsure of is the ISC, I did take it off and real quick I momentarily put voltage to it and it works, but I can’t read any voltage going to it when it’s back probed and running. Not sure if the ISC plays a roll in cold starting or not but figured I’d throw that in. Any help would be greatly appreciated! Thanks Travis. PS the dash pot is in good working order as well and I did clean the EGR valve itself but it doesn’t seem to want to stall out when I do the stall test..


RE: Cold start/idle Issue! - fixkick - 04-22-2019

hello Tquick;
yes these old cars are very hard to diagnose until 1996.
G16A TBi ENGINE.
1100 RPM MEANS VACUUM LEAKS, (LOTS OF PATH , LEGIT AND NOT)

THE ISC IS PWM MODULATED 100 TIMES A SECOND.
There are vast kinds of voltmters for 50 + years, even DMM meters many will see that 200Hz square wave as 0volts (blind to AC it is) scope sees truth never any dmm but say RMS meter.

hard starting and bad hot idle.
well are the spark parts fresh plugs wires and cap ./rotor or 25 year old.?


the IAC adds air cold , the ISC im not sure cold it is a hot running device, but may be open 50% at cold start.
The IAC air must happen or the engine wants to flood.
IAC is thermal in the base of the TB under 3 tiny screws (and cap)

isc signal some dmm show 7v 1/2 of alternator voltage others 0 or any wild thing, 7vdc is averaging of a square wave.
http://www.fixkick.com/IDLE-AIR/iac-wave1w.jpg


the ISC is here. pin B14, the other end of ISC is battery voltage (lite-green/red) lite-green-white wire is modulated by the ECU 200 times a second.
http://www.fixkick.com/INJECTORS/89/89-90schem1.jpg


RE: Cold start/idle Issue! - fixkick - 04-22-2019

i'd first diagnose this way. RPM hot.
first off is the ECU blinking code 12s hot and cold engine (use the diagnostic jumper on the DLC connector) 12means OK ECU happy.

does the engine reach 180F+ or more. hot. hand on top rad hose, hand flies off hot, and bingo for 180F ,at 160 or 150 or below hot , doomed to run bad.
then next is vacuum leaks.
make sure the IAC closed above 150F water temp 180f is spec for spec thermostat, make the thermostat works correctly first. (over 7 years old they fail)

any vacuum leaks hot ?you will get too high RPM with full power from the engine.
the tests for vacuum are tedious.... ask


RE: Cold start/idle Issue! - tquick79 - 04-22-2019

(04-22-2019, 04:59 AM)fixkick Wrote: hello Tquick;
yes these old cars are very hard to diagnose until 1996.
G16A TBi ENGINE.
1100 RPM MEANS VACUUM LEAKS, (LOTS OF PATH , LEGIT AND NOT)

THE ISC IS PWM MODULATED 100 TIMES A SECOND.
There are vast kinds of voltmters for 50 + years, even DMM meters many will see that 200Hz square wave as 0volts (blind to AC it is) scope sees truth never any dmm but say RMS meter.

hard starting and bad hot idle.
well are the spark parts fresh plugs wires and cap ./rotor or 25 year old.?


the IAC adds air cold , the ISC im not sure cold it is a hot running device, but may be open 50% at cold start.
The IAC air must happen or the engine wants to flood.
IAC is thermal in the base of the TB under 3 tiny screws (and cap)

isc signal some dmm show 7v 1/2 of alternator voltage others 0 or any wild thing, 7vdc is averaging of a square wave.
http://www.fixkick.com/IDLE-AIR/iac-wave1w.jpg


the ISC is here. pin B14, the other end of ISC is battery voltage (lite-green/red) lite-green-white wire is modulated by the ECU 200 times a second.
http://www.fixkick.com/INJECTORS/89/89-90schem1.jpg

I should say it runs great and idles smooth when warm but it does stay around the 1100 mark, but is it possible that the tach in not accurate?


RE: Cold start/idle Issue! - tquick79 - 04-22-2019

(04-22-2019, 05:05 AM)fixkick Wrote: i'd first diagnose this way. RPM hot.
first off is the ECU blinking code 12s hot and cold engine (use the diagnostic jumper on the DLC connector) 12means OK ECU happy.

does the engine reach 180F+ or more. hot. hand on top rad hose, hand flies off hot, and bingo for 180F ,at 160 or 150 or below hot , doomed to run bad.
then next is vacuum leaks.
make sure the IAC closed above 150F water temp 180f is spec for spec thermostat, make the thermostat works correctly first. (over 7 years old they fail)

any vacuum leaks hot ?you will get too high RPM with full power from the engine.
the tests for vacuum are tedious.... ask

I’ll check all this stuff. I’m willing to try anything I just want it to run right. Lol.... I did install a new radiator and new hoses sonis it possible there are air bubbles caught in the system causing problems? And also is there a rebuild kit or something for the IAC. I guess it’s possible that that is letting air by.


RE: Cold start/idle Issue! - fixkick - 04-22-2019

no kits for IAC , just new or used TBI body.

why not do the CeL lamp tests, with a paper clip. (unbent)

http://www.fixkick.com/CEL/CEL.html#OBD1codes


RE: Cold start/idle Issue! - tquick79 - 04-22-2019

(04-22-2019, 08:29 AM)fixkick Wrote: no kits for IAC , just new or used TBI body.

why not do the CeL lamp tests, with a paper clip. (unbent)

http://www.fixkick.com/CEL/CEL.html#OBD1codes

I will do that when I get home tonight and let you know the outcome.. thanks again!


RE: Cold start/idle Issue! - tquick79 - 04-22-2019

(04-22-2019, 09:51 AM)tquick79 Wrote:
(04-22-2019, 08:29 AM)fixkick Wrote: no kits for IAC , just new or used TBI body.

why not do the CeL lamp tests, with a paper clip. (unbent)

http://www.fixkick.com/CEL/CEL.html#OBD1codes

I will do that when I get home tonight and let you know the outcome.. thanks again!
So I did the paper clip test and all I got was all 12s.


RE: Cold start/idle Issue! - fixkick - 04-22-2019

hot and cold engine both, you can even drive while its flashing. and it flashes 12, or errors.
this trick catches intermittent bad sensors.
does engine have full power driving on the road and up hills.?
does the tail pipe end smoke , black or white?
on old car like this G16a
Id first do basics, make sure the front crank bolt 17mm socket sizes is set to 94fl/lbs. , in 5th gear,brakes set hard. that saves damage to the crank cog up front. (i think you did)
then check compression 150psi x4 , wot, wide open throttle done or over 1/2 way throttle, so engine can suck air.
then check fuel pressure. at the filter, test port, banjo fitting 6mm threaded screw.
make sure the map hoses are not clogged end for end. the map must receive full vacuum at all times, from the intake plenum. or it will never run right.

do the clay test in on the IAC?
check all vacuum holes for leaks.? (the pinch test)
the TV stop screw , if you unscreew it hot engine, does the RPM drop to 800? if not the engine does have a vacuum leak, only where is the question. (lots of ways)

the are 3 ways to prove thermal IAC is bad hot engine, the 2 clay tests or the false base gasket. test.
pack this hole, and if hot idle is
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/cold-air-n2bw.jpg

or pack this full. of clay. (or electrical mastic putty we call monkey poop , never gets hard this stuff)
see this 3 hole cavity, pack this in clay and IAC is dead. (Idle go 800 or less now?
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/cold-air2w.jpg

last the gasket trick


this one is super bad
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/90-TB-bottom1.jpg

the 5 holes on the right must never be UN blocked by the gasket, the gasket must be solid there.
the H2o hole is blocked the IAC goes dead, stuck open forever.
the air hole is the IAC output, to the plenum. this can be blocked as test (custom gasket hand made) and if idle goes below 800 you found your leak (hot engine)

now keep in mind if you do block the IAC cold starts will want to flood so you must use right foot pressed say 5% to keep engine running and if when hot engine the idle is still high
there is a huge vacuum leak and is NOT the IAC.
we pinch hoses to find leaks or find cracked hoses the vacuum booster or is hose can leak air, and is more hard to block but can be done, but power brakes will be dead so dont drive.
the booster it self can leak.
the EGR base gasket can leak and suck air, there are many points in to this engine that can leak air causing vacuum leak and high idle even with TV stop screw CCW backed off.
ever clean the TV valve? it too can gunk up and not close.

the order i do this is by difficulty , all on a hot engine 180f+} water coolant temperatures.
1: Pinch hoses is so simple if idle drops bingo (do not pinch map hose, inspect ever inch and both nipples and make sure the far end sucks are when pulled off map.
pulling the map hose running will flood the engine so just know that. just make sure the map receives vacuum live.
2: close the TV valve, by turning the stop valve CCW and make sure it closes full,with
3: block the brake booster hose pipe with a cork. diskconnected (most easy way is that) large hose. idle ok now?
4: you can also block the ISC up top with fake solid gasket. idle ok now, below 1100 but goal is 800 or less hot, for sure less with ISC now dead.
5: clay block the IAC. this is the last normal idle air supply, once blocked NOW there is no air now.(cant run engine,.now unless fancy right foot actions(pressings)
6: once here the airless engine should stall due to lack of all air inducted. zero air and too much fuel if stalls.
7: bad gaskets under TBI body, or intake to head gasket 4 ports leaking, or loose intake manifold bolts.

I think i did all leaking paths for vacuum above. correct me if I missed any.
good luck to you.
but 1100 RPM hot is wrong. need to be found this leak.


RE: Cold start/idle Issue! - tquick79 - 04-22-2019

(04-22-2019, 10:03 PM)fixkick Wrote: hot and cold engine both, you can even drive while its flashing. and it flashes 12, or errors.
this trick catches intermittent bad sensors.
does engine have full power driving on the road and up hills.?
does the tail pipe end smoke , black or white?
on old car like this G16a
Id first do basics, make sure the front crank bolt 17mm socket sizes is set to 94fl/lbs. , in 5th gear,brakes set hard. that saves damage to the crank cog up front. (i think you did)
then check compression 150psi x4 , wot, wide open throttle done or over 1/2 way throttle, so engine can suck air.
then check fuel pressure. at the filter, test port, banjo fitting 6mm threaded screw.
make sure the map hoses are not clogged end for end. the map must receive full vacuum at all times, from the intake plenum. or it will never run right.

do the clay test in on the IAC?
check all vacuum holes for leaks.? (the pinch test)
the TV stop screw , if you unscreew it hot engine, does the RPM drop to 800? if not the engine does have a vacuum leak, only where is the question. (lots of ways)

the are 3 ways to prove thermal IAC is bad hot engine, the 2 clay tests or the false base gasket. test.
pack this hole, and if hot idle is
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/cold-air-n2bw.jpg

or pack this full. of clay. (or electrical mastic putty we call monkey poop , never gets hard this stuff)
see this 3 hole cavity, pack this in clay and IAC is dead. (Idle go 800 or less now?
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/cold-air2w.jpg

last the gasket trick


this one is super bad
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/90-TB-bottom1.jpg

the 5 holes on the right must never be UN blocked by the gasket, the gasket must be solid there.
the H2o hole is blocked the IAC goes dead, stuck open forever.
the air hole is the IAC output, to the plenum. this can be blocked as test (custom gasket hand made) and if idle goes below 800 you found your leak (hot engine)

now keep in mind if you do block the IAC cold starts will want to flood so you must use right foot pressed say 5% to keep engine running and if when hot engine the idle is still high
there is a huge vacuum leak and is NOT the IAC.
we pinch hoses to find leaks or find cracked hoses the vacuum booster or is hose can leak air, and is more hard to block but can be done, but power brakes will be dead so dont drive.
the booster it self can leak.
the EGR base gasket can leak and suck air, there are many points in to this engine that can leak air causing vacuum leak and high idle even with TV stop screw CCW backed off.
ever clean the TV valve? it too can gunk up and not close.

the order i do this is by difficulty , all on a hot engine 180f+} water coolant temperatures.
1: Pinch hoses is so simple if idle drops bingo (do not pinch map hose, inspect ever inch and both nipples and make sure the far end sucks are when pulled off map.
pulling the map hose running will flood the engine so just know that. just make sure the map receives vacuum live.
2: close the TV valve, by turning the stop valve CCW and make sure it closes full,with
3: block the brake booster hose pipe with a cork. diskconnected (most easy way is that) large hose. idle ok now?
4: you can also block the ISC up top with fake solid gasket. idle ok now, below 1100 but goal is 800 or less hot, for sure less with ISC now dead.
5: clay block the IAC. this is the last normal idle air supply, once blocked NOW there is no air now.(cant run engine,.now unless fancy right foot actions(pressings)
6: once here the airless engine should stall due to lack of all air inducted. zero air and too much fuel if stalls.
7: bad gaskets under TBI body, or intake to head gasket 4 ports leaking, or loose intake manifold bolts.

I think i did all leaking paths for vacuum above. correct me if I missed any.
good luck to you.
but 1100 RPM hot is wrong. need to be found this leak.

Thanks so much for helping me with this! I’m off work a few days this week and will try all the above things you mentioned and let you know what I find. Thanks for the timely responses!