2.3l timing belt and ECM change: won't idle

[jenkytrucks]

Actively workin on this, I live in OR and rain is coming!

Got an 89 2.3l 4x4 that needs to get down the road/off the sidewalk! The story thus far: 2 weeks ago, took it out to the woods, parked it, few hrs later it cranked but wouldn't start up. After diagnosin it myself and gettin inconsistent spark for a few days, got it towed outta there to a shop.

Took em 2 weeks to find out that it was a bad ECM/PCM.They replaced it twice. 2nd time they are now getting consistent spark. But won't turn over. So they tell me the timing belt has slipped and that's why it won't start, but the computer was bad and I still needed that too.

So I couldn't afford havin them do the belt, so I take it home and did it myself. This is my first time doing it. Did it by the book/forum, Cam and crank are still aligned after 2 rotations, put it all back together, now it starts fine but won't idle. Have to give it gas or it dies. Fuel filter is new, can't see any disconnected vacuum lines, cleaned the MAF and IAC, replaced S-belt. Haven't put the fan back on yet.

I can't seem to find any posts with this exact problem, a lot of rough idles from a tooth being off, but I'm pretty certain that my teeth are lined up correctly.

Any help would be great.

 

[RonD]

Get another mechanic

ECM/PCM(computer) doesn't control the spark in '89, that didn't happen until '95 when newer EEC-V computer was used(OBDII)

ICM(ignition control module) located on the front of the intake manifold runs the spark.
ICM gets spark advance and retard "suggestions" from ECM but can run spark without ECM input.
2.3l ICM's did have issues, worn wiring, loose connectors and general failure.
Spark system is:
CKP(crank position) sensor, it tells ICM when #1 piston is at TDC, it reads crank's "tone wheel"
ICM gets the CKP sensor pulses, then grounds and ungrounds coil packs to spark in the correct firing order

Coil packs, dual coil packs are used to reduce emissions, but(THIS IS IMPORTANT), only the exhaust side coil pack works when starting engine, so there is NO SPARK on intake side spark plugs when cranking engine, this is NORMAL.
Intake side coil pack is used after engine RPMs are above 500.
So when testing for spark you need to test Exhaust side only
This also means if exhaust side coil pack fails you get a no start

Fuel injected engines can't use "idle screws" like carbs had, there are no jets to add more fuel when you adjust the idle, so an idle screw could damage engine by running it too lean.
An IAC(idle air control) valve is used instead, this allows the ECM to adjust idle and increase/decrease fuel as needed for RPM.
To determine if IAC valve is working, start cold engine, RPMs should go up above 1,600 then drop down to about 1,200, thats the ECM opening IAC valve all the way and then closing it a bit to set Cold Engine Idle
As engine warms up RPMs should slowly drop to 700-800 for Warm Engine Idle.

If this isn't happening then IAC valve needs to be cleaned or hooked up correctly.
Pull off IAC Valve and hook up electrical connector, turn key on, valve should open all the way, turn key off and it should close, repeat a few times.
Also clean MAF sensor, this should be done every few years.

On the drivers side of the block toward the front is the ECT(engine coolant temp) sensor, ECM uses this to determine if engine is cold or warm, it is a 2 wire sensor, not to be confused with the 1 wire SENDER used for dash board temp gauge.
If ECT was disconnected you should get a CEL on just after starting.
Or after engine warmed up it would idle OK, but this doesn't sound like that.

 

[enjr44]

Glad to see your back Ron.

 

[jenkytrucks]

I know that on this DIS system only the exhaust side needs to fire to start it up. When diagnosing the spark prior to ECM replacement, there was inconsistent firing on exhaust side (all 4 cylinders would fire and then #4 wouldn't or #2 or #1 etc). I personally also tested both ground and power to ICM and took it to Napa to have them test it. It tested good, and both coil packs had close to brand new terminal to terminal ohm resistance when I measured them with a multimeter.

So, I have already cleaned both the IAC and the MAF, and I never disconnected the eng temp sensor when I did timing job: just loosened that hose and swiveled it outta the way.

After some more research, I'm wondering if perhaps the new ECM needs to "relearn" the idle? or maybe I have a faulty crank position sensor? But if it was the Crank pos sensor then I wouldn't be getting spark correct?