Let's play - diagnose the Cavalier for Todd

[tjthorson]

You do know that some of the early model GM computers had an "Idle Learn Procedure" they needed to go through whenever the ECM lost battery power, don't you?

Yes - thanks. I have done that multiple times.

I have also now thrown a new O2, MAP, and dropped the TPS to .38.

I have one more thing that looks interesting. In my OTC4000 - there is a parameter "3rd Gr Sw" - it is always "on"

Is there some code in the ECM that detects 3rd gear from the trans and maybe tells the IAC to add air so if you let off the gas on the highway it doesnt slow the car way down like if you hit the brakes. The trans seems operationally fine - all the gears are crisp and the TCC locks and the OTC confirms that. But that "3rd gear sw" is always on - even when in park (which the ECM confirms proper operation of the P/N switch)

A/C request is "no" and I cannot find any power steering request....
If that is the case - is there a way to unplug/remove that switch or is it in the valve body? Maybe someone knows which wire going into the ECM it is and I can cut it to test?

 

[John Larkin]

If there is a plug on the outside of the transmission, you could unplug it and then none of the switches would be "on", right? Free to try it anyhow.

 

[SloGN]

i know that some of the older gm ecm required you to drive the car for a tad bit over 40 mph to do the idle reset thing. I had this problen on my 85 pontiac fiero 2.8 car. i replaced the idle valve several times till i found that out from.

 

[tjthorson]

I drove it to work today, had quite a few miles up to and including 55mph. I also grabbed the IAC out of the Fiero just in case the Napa one was bad/wrong.... Still 1500rpm idle....

I am going to drive it for a few days.... Need to get a muffler put on it - running s straight pipe now...

i know that some of the older gm ecm required you to drive the car for a tad bit over 40 mph to do the idle reset thing. I had this problen on my 85 pontiac fiero 2.8 car. i replaced the idle valve several times till i found that out from.

 

[SloGN]

I drove it to work today, had quite a few miles up to and including 55mph. I also grabbed the IAC out of the Fiero just in case the Napa one was bad/wrong.... Still 1500rpm idle....

I am going to drive it for a few days.... Need to get a muffler put on it - running s straight pipe now...

are you sure it's idling that fast or is the tach reading a little high?


have you ever checked the base idle screw to see if it has been messed with. also i think the older 2.0 had a dist. check the timing to see if it's correct?

 

[tjthorson]

are you sure it's idling that fast or is the tach reading a little high?


have you ever checked the base idle screw to see if it has been messed with. also i think the older 2.0 had a dist. check the timing to see if it's correct?

Its for sure high... it was at 3000 originally when I bought the car.

base timing has been set and reset - this is a whole new long block.

I am 1500 rpm in park cold or warm according to the ECM on the scantool. dash gauge is close.

 

[Pablo]

Have you gone through the minimum idle set procedure?

you need to jumper the ALDL long enough for the IAC to bottom out (usually A and B in the ALDL port, same procedure to display codes). Look into the iac air hole and verify this visually. Once that is done, disconnect the IAC, turn the key to the off position, remove the jumper from the ALDL port.

Now attempt to start the car. It may not want to start or hold an idle, if it doesn't, you'll need to turn in the idle screw on the side of the TB so that the throttle blades are further open.

Eventually the car should start and run. Your service manual should specify what the minimum idle should be on your car. You then adjust the idle screw to this rpm. I personally like to err on the high side so the IAC has less counts at idle. This is especially important on a TBI setup for a number of reasons.

Give it a shot.

 

[tjthorson]

This one is new.... if this works... Pablo my friend... You will have to send me a paypal address so I can buy you lunch...

The idle set procedure I had found was.... warm up vehicle - disconnect battery for 20 secs. reconnect and start vehicle. let run 5 minutes. turn vehicle off.

What you are describing certainly seems like it would do more...

My minimum set screw is capped still.... i will try this tonight and report tomorrow.

Have you gone through the minimum idle set procedure?

you need to jumper the ALDL long enough for the IAC to bottom out (usually A and B in the ALDL port, same procedure to display codes). Look into the iac air hole and verify this visually. Once that is done, disconnect the IAC, turn the key to the off position, remove the jumper from the ALDL port.

Now attempt to start the car. It may not want to start or hold an idle, if it doesn't, you'll need to turn in the idle screw on the side of the TB so that the throttle blades are further open.

Eventually the car should start and run. Your service manual should specify what the minimum idle should be on your car. You then adjust the idle screw to this rpm. I personally like to err on the high side so the IAC has less counts at idle. This is especially important on a TBI setup for a number of reasons.

Give it a shot.

 

[Pablo]

if that doesn't work I would lean toward a vacuum leak (even though you have looked sometimes they can be tricky to find)

TBIs are notorious for tbi to intake manifold leaks

beyond that, I would look for a leaky injector pod or sticking injector. A leaky injector pod will look like fuel just dripping out of the injector pod and youll be able to see this by just turning the key to the on position and letting the fuel pump prime while at the same time looking at the injector. If you see fuel drip out then you have a faulty injector o ring.

To see if your injector is sticking, look at what your fiero's injector looks like at idle and if the cavalier's looks drastically different (like a much heavier plume or an irregular pulsation) it could be a sticking injector. TBI injectors are very reliable though and I've never seen that happen.

 

[SloGN]

Its for sure high... it was at 3000 originally when I bought the car.

base timing has been set and reset - this is a whole new long block.

I am 1500 rpm in park cold or warm according to the ECM on the scantool. dash gauge is close.

did you unhook the check connector before atempting to adjust the base timing?. one other thing to check is the egr circuit.

 

[tjthorson]

Well - I performed Pablos procedure.

It was hard to tell if the IAC had bottomed out because all you can see from the top of the TBI os where the air goes in - not the plunger itself.

I still have thos NOID IAC checker things on the way - when they get here I will report back.

After Pablos procedure.... it started slow, and within a few seconds was at 2000 rpm.....

IAC counts are like 100-110.....

So... no lunch for you Pablo.... Thanks anyway though.

I do have some TBI base gaskets ordered. This thing had a goofy spacer thing which what looked like a heating coil on it.... The foil on the spacer is kinda torn in spots, but not where it seals... I also noticed that spacer is fuel soaked and soft where the foil is gone.... I am going to remove that whole thing, put in a regular gasket and try again.

My minimum idle screw seems to be way out - like the butterfly is barely open.... Should i crank it up? Would that theroetically bring down the IAC counts - and the idle speed? My suspicion is I would be replacing IAC air with throttle body air and the idle speed would remain the same....

Unless anyone has anything new to add, ill report back when I get those gaskets in....

 

[Scott Atk]

Todd, you mentioned that you couldn't find any power steering info on your scan tool. Is there a switch on the power steering pressure line? If so, maybe disconnect?
As you know the ECM is commanding the high idle for some reason as indicated by your high IAC #'s
I would think a vacuum leak would show low or zero IAC #'s

 

[Pablo]

if the min. idle screw is way out then you almost certainly have a vacuum leak.

Were you able to establish the correct idle with the IAC disconnected and bottomed out?

If so, you can disconnect the IAC and drive it without the IAC connected. The IAC isn't really that necessary. It can make starting take a couple of tries first thing in the morning but other than that if you set your min idle high enough to avoid stalls on gear selection, you'll never notice it was gone.

On my Firebird I disconnected it and never looked back. Trying to tune it to work with a big cam was impossible. Never missed having it either.

 

[tjthorson]

if the min. idle screw is way out then you almost certainly have a vacuum leak.

Were you able to establish the correct idle with the IAC disconnected and bottomed out?

If so, you can disconnect the IAC and drive it without the IAC connected. The IAC isn't really that necessary. It can make starting take a couple of tries first thing in the morning but other than that if you set your min idle high enough to avoid stalls on gear selection, you'll never notice it was gone.

On my Firebird I disconnected it and never looked back. Trying to tune it to work with a big cam was impossible. Never missed having it either.

OK - thanks for helping. Back in the beginning, I pulled the plunger out on the IAC, put it back in and left it unplugged. The car wouldnt idle at all - just small sputters, which *I thought* told me I DIDNT have a vacuum leak.

I will try manually setting the idle. I have to pry off the cap off the min idle set screw. I am wondering if everything else (fuel, ignition timing, etc) will still work, or will it set a CEL and put the car in "limp mode".

I did find a switch and plug on the power steering pump line, back along the firewall - disconnecting and reconnecting it has no effect on the idle.

The NOID lights came today - I hooked up the IAC checker, turned the key to on - and have 1 green and 1 red LED. I assume that means the IAC signal and wiring is fine....

Turning the key to "on" and hearing the fuel pump prime - there are no drips or leaks from the injector pod. It does have a nice cone spray, no drips or uneven spraying.

Tomorrow afternoon after work I will manually set the idle and see how it goes.... The big push to get this thing on the road is this $4 gas pricing. Even the 1984 technology has to be better then the 4.7v8 in my wife's jeep commander....

 

[SloGN]

when you checked the base timing did you unhook the check connector to put it in base timing mode? it's really acting like the timing is too high?

 

[tjthorson]

when you checked the base timing did you unhook the check connector to put it in base timing mode? it's really acting like the timing is too high?

Well. No... I couldnt find any single wire type thing that would have appeared to be a connector for that purpose. There is 3 connectors going to the distributor. I unhooked the one that appeared to be a control type (not power or ground) - it was a 4 pin weatherpack connector - and the car wouldnt start.

What I did do was put it into "check code" mode by putting a wire between pins 1-2 on the ECM connector - then I set the base timing...

If that wasnt right... that would certainly explin my problem (except when i bought the car it had this same problem - so the PO (which only had shop work done - it was a 17 year old girl that inherited the car from her grandmother) would have had the timing off as well....

 

[SloGN]

Well. No... I couldnt find any single wire type thing that would have appeared to be a connector for that purpose. There is 3 connectors going to the distributor. I unhooked the one that appeared to be a control type (not power or ground) - it was a 4 pin weatherpack connector - and the car wouldnt start.

What I did do was put it into "check code" mode by putting a wire between pins 1-2 on the ECM connector - then I set the base timing...

If that wasnt right... that would certainly explin my problem (except when i bought the car it had this same problem - so the PO (which only had shop work done - it was a 17 year old girl that inherited the car from her grandmother) would have had the timing off as well....

well i think that you need to get a repair manual and look thru it for the timing procedure. when checking the timing when you unhook that wire it takes the ecm out of the loop and it will set a code 42 EST if i remember correctly. I will try and go by my buddy shop to day and look theis info on alldata to get eh info on how to set the timing the correct way.

 

[tjthorson]

I guess I will consider this issue closed. Thank you to all that tried to help.

I ended up bottoming out the IAC and unplugging it. I pulled the cap and cranked up the min idle speed screw to about 950rpm in park (750 in drive). After it warmed up, it was idling in park at about 1050rpm or so. Good enough for me.

Idles nice and smooth, I reset the TPS then to .46.

I left the OTC plugged in - the ECM is still commanding 90-110 IAC counts all the time - but its running fine, O2 switching between rich/lean, drives nice, idles smooth - so I'll let it go for now. Maybe someday Ill figure out what it was.

Thanks again!

 

[gunslinger]

Tsb

There's a TSB for this:

Number: 84-273-6E

Section: 6E

Date: Nov., 1988
Subject: SLIGHTLY HIGHER IDLE SPEED

Model and Year: 1983-84 CAVALIER WITH 2.0L TBI (VIN CODE P) ENGINE AND POWER STEERING
TO: ALL CHEVROLET DEALERS


Condition:

Idle speed in the range of 1200 to 1625 RPM, in closed loop, in park or neutral, with the steering wheel not fully locked either right or left, may be experienced. This slightly raised idle speed has no adverse affect on driveability or vehicle performance, but may be objectionable from a noise standpoint.
Cause:

An open circuit in the signal to the Electronic Control Module (ECM) from the power steering pressure switch. Unlike the 1985 and later models which use a normally OPEN switch, the 1984 and earlier J-cars with the 2.0L engine use a normally CLOSED power steering pressure switch. If the ECM sees an open at any point in this circuit, it will interpret the open as a power steering load, and will raise the idle speed.
Correction:

Disconnect the power steering switch. If there is no change in idle speed, this condition is the cause of slightly higher idle and the switch should be replaced. If the idle speed changes, the cause of the higher idle speed should be investigated through normal diagnostic methods.
Refer to the 1984 Service Manual, pages 6E2-76 and 77, which is the Idle Air Control (IAC) Diagnostic Chart. The wiring diagram will lead to possible areas which may be open in the circuit, such as an open power steering pressure switch, an open A/C compressor clutch coil, an open A/C high pressure switch, an unplugged connector, loose ground connections, or a cut or pinched wire. Repair as necessary.



Straight from alldata

 

[tjthorson]

This was awesome - I saw this come through my Blackberry while I was at the YMCA working out today. I ran out to the parking lot and used a jumper wire on that plug.... No change in IAC counts.

I am going to replace the switch anyway - and report back. Thanks!

Todd

There's a TSB for this:

Number: 84-273-6E

Section: 6E

Date: Nov., 1988
Subject: SLIGHTLY HIGHER IDLE SPEED

Model and Year: 1983-84 CAVALIER WITH 2.0L TBI (VIN CODE P) ENGINE AND POWER STEERING
TO: ALL CHEVROLET DEALERS


Condition:

Idle speed in the range of 1200 to 1625 RPM, in closed loop, in park or neutral, with the steering wheel not fully locked either right or left, may be experienced. This slightly raised idle speed has no adverse affect on driveability or vehicle performance, but may be objectionable from a noise standpoint.
Cause:

An open circuit in the signal to the Electronic Control Module (ECM) from the power steering pressure switch. Unlike the 1985 and later models which use a normally OPEN switch, the 1984 and earlier J-cars with the 2.0L engine use a normally CLOSED power steering pressure switch. If the ECM sees an open at any point in this circuit, it will interpret the open as a power steering load, and will raise the idle speed.
Correction:

Disconnect the power steering switch. If there is no change in idle speed, this condition is the cause of slightly higher idle and the switch should be replaced. If the idle speed changes, the cause of the higher idle speed should be investigated through normal diagnostic methods.
Refer to the 1984 Service Manual, pages 6E2-76 and 77, which is the Idle Air Control (IAC) Diagnostic Chart. The wiring diagram will lead to possible areas which may be open in the circuit, such as an open power steering pressure switch, an open A/C compressor clutch coil, an open A/C high pressure switch, an unplugged connector, loose ground connections, or a cut or pinched wire. Repair as necessary.



Straight from alldata