Let's play - diagnose the Cavalier for Todd

[tjthorson]

So... I spent $600 and picked up this 1984 Chevy Cavalier for the wife to play with in the summer.... Its a red convertible, 2.0 automatic, F-41 sport suspension. Get this - only 51,000 original miles. Two small bubbles in the paint - no rust of really any kind. Had the "Rusty Jones" treatment - this waxy film is all over EVERYTHING.

Power top, windows, cruise, air, all work...

Anyway - here is the deal. Every gasket on the engine leaked... - So I opted to pull it and freshen it up. I drove it home when I bought it - the thing I noticed was the idle was REAL high. Like - 2500-3000rpm cold, warm, etc. No CEL.

I thought I found a cracked vacuum line and repaired it - no dice. i just figured since the gaskets were all dried up - the intake was leaking too - so I went about pulling the engine. In the process of ordering up parts - I stumbled across a complete rebuild longblock on ebay for $400. That was cheaper then the rings/gasket set/oil pump/timing set i was going to buy - so i bought the long block.

So - now I have a totally different long block. This thing still races. I have replaced the ECM. The only thing left in the mix that is original from the old engine is the intake and TBI unit. I have already cleaned and then replaced the IAC solenoid. It runs nice and smooth - not rich, no sputtering - just at 2500 rpm at "idle".

Other then now replacing the TBI unit - is there anything else I can check? I do have a OTC4000 I can fire up. Everything looked OK when i checked - TPS at .49, O2 was registering and "changing".

What the heck am I missing here. Trying to get this toy road worthy for the wife. TIA!

 

[TurboJim]

What are your IAC counts? BLM? Pull the IAC out and see if its extended or retracted. If Extended, you have a vacuum leak. Squeeze off the PCV hose, squeeze off the booster hose. Dont bother with the small hoses as 2500rpm is a large leak. If the IAC is retracted, pull it out a bit and carefully install it. If it bottoms before being screwed all the way in you'll break it off if you force it. Leave it unplugged and start it. If the idle is now low, you need to check the IAC wiring for a break. If you dont mind spending a couple bucks get ATD's noid light set with the IAC checker. You can get the set for like $40 at most auto parts stores (you may have to order it) and verify the PCM is changing polarity and can actually supply the IAC with current in reverse. Also another possibility is an open CTS, but the thing would be pig rich as open the CTS will read -40*.

Did you pull the throttle body off the intake when you redid the engine? Its common for them to suck in the gasket causing a high idle. While 2500 is kinda high for a TB gasket leak and you should be able to HEAR a leak that large, it might be worth a look if all else fails. Just think methodically about this one and you'll have it licked in no time.

 

[John Larkin]

Take a propane torch and just turn on the gas without lighting it. Move the end around the various mating points of the intake. If there's a leak, the extra fuel should increase the RPM even further. Not wishing you bad luck but the intake might even have a crack somewhere.

 

[tjthorson]

Sorry I took so long.... Needed some nice weather to get back out there....

So...
The IAC plunger was all the way in (couldnt see any gap between the coils of the spring). Pulled it out and reinstalled it. Left it unplugged - have a really low idle, wouldnt stay running. Back off the plunger a bit (hoping for manual idle adjustment ) And back up to 2000 rpm. Plugged IAC back in - idle actually dropped to about 1800, then went back up to 2100 - but didnt go back up to 3000 rpm

Hook up the OTC4000E. Let it run from cold all the way to thermostat opening. Any values that changed when warm are noted:

IAC - 77
INT - 128
O2 - .16 up to .65 once in closed loop
O2CC - 2 up to 6 changes constantly
MAPV - 1.24 up to 1.3 warm
RPM - 2025 - 2100
COOL - 092
CODE - NO
MAP - 033 then warm 032
TPS - .46
BLM - 127

Now.... remember another thing you noted - i pinched off the brake booster vacuum - no change. Pinched off the PCV, idle dropped some.... to about 1700. Pulled the pcv valve out and capped it with a piece of duct tape.

Now - it idles at 1275-1300.

Maybe it helps too - it does hit closed loop - does flip from lean to rich, fan turns on when it hits 22 on the gauge, etc....

With the PCV capped off, at 1275 RPM, this value changed:
MAPV - 1.84
All the others were pretty much the same. It read "lean" until it warmed up, i saw the thermostat open (temp dropped) and it hit closed loop. Then it started flipping from lean to rich.

So.... Now what? Thanks Jim - I had hoped you would come to my rescue....

John... thanks. went around with a propane torch - couldnt find anything.....

 

[John Larkin]

Throttle blade closing all the way? Can you remove the TBI and shine a light on the backside to look for a gap?

 

[tjthorson]

Throttle blade closing all the way? Can you remove the TBI and shine a light on the backside to look for a gap?

Heck, I dont know, it appears to be.

I thought I had it. I cleaned the IAC port again - tons of black stuff came out, and it seemed to be fine around 1200 with 900 in drive.

Even though it was still a little high, I got excited, and proceeded to rip the front end apart and replace the front CV axles and rotors and pads. Put it all back together....

2500RPM.....

I am leaning toward replacing the TBI with a junkyard one. I know Jim would bash me for being a "parts changer" - but I think it has to be in there.

One new development - I am getting voltage on all 4 wires at the IAC. 2 are 14v - the other 2 are .60 volts (or so.) Dont know if thats good or bad - but at least I may not have a broken wire.

EDIT: I just had a thought. Also in the backyard is my daughters car.... 1984 Fiero - 2.5TBI. If I swap the injector - are those TBI units the same? Wonder if I could use that for testing.....

 

[John Larkin]

Heck I'd try the swap. Why not?

 

[SloGN]

the injector on the 2.5l fiero is gonna be a tad bigger than the 2.0l one. but the base tbi is the same.

 

[Tony Shoaff]

High Idle

Start the engine and spray some carb cleaner around the intake and t_body area. If the ldle changes there is your vacuum leak causing a fast idle. A bad ecm can cause a fast idle also. Good luck.

 

[tjthorson]

Start the engine and spray some carb cleaner around the intake and t_body area. If the ldle changes there is your vacuum leak causing a fast idle. A bad ecm can cause a fast idle also. Good luck.

Thanks Tony.

Replaced ECM - that was my thought too initially.

The only spray of carb cleaner that changes the idle is when I soak where the IAC pulls its air on the top back right corner of the TBI unit - or directly down the throttle body (of oourse)

These are all new gaskets and I had the intake out and looked it over when I put the longblock in.

Dont have time today - but next chance I get, I am going to pull the TBI on the fiero, swap the injector and try it....

 

[TurboJim]

Well, if pulling the IAC pintle out results in a low idle, then the capability to control idle is there. Now we need to know WHY the IAC is commanded 77 counts when the desired idle should be 700 or whatever rpm. My problem with the vacuum leak theory is the ECM could be commanding low or 0 counts if it wanted a 700rpm idle and idle was at 2000rpm. Is the power steering switch closed? Is there an AC request? Is the cooling fan showing commanded on? What other cause for a commanded high idle do you see? CTS reading about right? Is VSS showing 0mph?

I'd like to see if there is a break in the wiring to the IAC, maybe its OK in one direction, but the other has a break? That doesnt explain the 77 counts though.

Sorry I cant be of more help. Its tough to see what you see from my kitchen table. If you bring the car to me, I'm sure I can fix it in no time. :-P

 

[tjthorson]

Well, if pulling the IAC pintle out results in a low idle, then the capability to control idle is there. Now we need to know WHY the IAC is commanded 77 counts when the desired idle should be 700 or whatever rpm. My problem with the vacuum leak theory is the ECM could be commanding low or 0 counts if it wanted a 700rpm idle and idle was at 2000rpm. Is the power steering switch closed? Is there an AC request? Is the cooling fan showing commanded on? What other cause for a commanded high idle do you see? CTS reading about right? Is VSS showing 0mph?

I'd like to see if there is a break in the wiring to the IAC, maybe its OK in one direction, but the other has a break? That doesnt explain the 77 counts though.

Sorry I cant be of more help. Its tough to see what you see from my kitchen table. If you bring the car to me, I'm sure I can fix it in no time. :-P

I hear ya. I appreciate any help. I did check with a voltmeter and had voltage of around 14v on two of the wires and .6v on the other two. VSS is 0. I *think* the CTS is in celsius? It was around 90 when I finally looked at it - saw it going up to 100 - thermostat opened, back down to 90. A/C request for sure was 0. Not sure on the cooling fan - but I know it was turning on and off when it was warmed up.

Its really bugging me. Unfortunately - I have a ton of work to do on my Jeep because we leave on 4/25 for our first Jeep Jamboree this year. So - until I get that stuff done - the Cavalier has to sit.... Im going to stop and grab more throttle body gaskets and maybe switch that thing out with the fiero TBI and try it....

 

[Tony Shoaff]

Where did you get the new IAC? What about the ECM? I had this same issue 2 months ago and I replaced the IAC and no help. Sent to the dealer to make sure the ecm was bad and it was. They told me though the IAC was bad also and I had just bought it from Advance Auto Parts?

 

[Tony Shoaff]

I hate not fixing something I am involved with. Are you sure the idle screw has not been adjusted to make it idle fast. Maybe it had a bad IAC and the previous owner turned up the idle so it would not die?? Good luck and keep us posted.

 

[tjthorson]

Where did you get the new IAC? What about the ECM? I had this same issue 2 months ago and I replaced the IAC and no help. Sent to the dealer to make sure the ecm was bad and it was. They told me though the IAC was bad also and I had just bought it from Advance Auto Parts?

Thanks for the help. The ECM and the IAC came from napa. The IAC was new, and the ECM is a "refurb".

Ill hopefully be able to put more time in this weekend on it.... So, it will have to sit for a few days until i get back from Cinci....

 

[tjthorson]

Well. I had a few minutes to try and look at this again today. It looks like the TBI on the fiero is not quite the same...

I didnt want to use carb cleaner to find the leak and spray carb cleaner all over my newly painted engine. So, I used fogging oil from my boat.

The oil had no effect on the idle at all. i sprayed the entire outside of the throttle body and intake.

So - I pulled the throttle body to take a closer look at it. I noticed looking at it from the bottom that the IAC was wayyy "open" (retracted?) again. I reached inside there and seated the plunger (extended it all the way). I also noticed there really isnt much to those things. I checked for play in the shaft and butterfly, the tps looks good, the vacuum ports are clean....

So - I reinstalled it and left the IAC unplugged (remember its closed). It wouldnt start... A few "stumbles" was it. I plugged the IAC back in... It started up and idled. Perfectly. 900RPM. Idle was moving around a bit every 10-15 seconds like 100rpm or so either way. I took it for a drive. Went about 6 miles - filled up the tank (the gas in it is still from last year), and drove home. Pulled in the driveway, grinning ear to ear... and....

1500RPM in park. I am really at a loss. Trying to remember the numbers -

IAC is at 53. TPS at .46 coolant at 90 something - thats all I remember....

This is really bugging me. I did notice the ECM set a code 22 (low TPS). Could that really cause this?

The fact that if I leave the IAC closed up and then it wont run at all really has me thinking its NOT a vacuum leak... This is some sensor confusing the ECM? So - what can have that effect? MAP? Temp? TPS? There isnt much on this thing, and I am at a loss. Should I try another IAC? Replace the TPS?

 

[TurboJim]

Well. I had a few minutes to try and look at this again today. It looks like the TBI on the fiero is not quite the same...

I didnt want to use carb cleaner to find the leak and spray carb cleaner all over my newly painted engine. So, I used fogging oil from my boat.

The oil had no effect on the idle at all. i sprayed the entire outside of the throttle body and intake.

So - I pulled the throttle body to take a closer look at it. I noticed looking at it from the bottom that the IAC was wayyy "open" (retracted?) again. I reached inside there and seated the plunger (extended it all the way). I also noticed there really isnt much to those things. I checked for play in the shaft and butterfly, the tps looks good, the vacuum ports are clean....

So - I reinstalled it and left the IAC unplugged (remember its closed). It wouldnt start... A few "stumbles" was it. I plugged the IAC back in... It started up and idled. Perfectly. 900RPM. Idle was moving around a bit every 10-15 seconds like 100rpm or so either way. I took it for a drive. Went about 6 miles - filled up the tank (the gas in it is still from last year), and drove home. Pulled in the driveway, grinning ear to ear... and....

1500RPM in park. I am really at a loss. Trying to remember the numbers -

IAC is at 53. TPS at .46 coolant at 90 something - thats all I remember....

This is really bugging me. I did notice the ECM set a code 22 (low TPS). Could that really cause this?

The fact that if I leave the IAC closed up and then it wont run at all really has me thinking its NOT a vacuum leak... This is some sensor confusing the ECM? So - what can have that effect? MAP? Temp? TPS? There isnt much on this thing, and I am at a loss. Should I try another IAC? Replace the TPS?

Yes Todd, just like our Buicks, this could cause a high idle as the ECM is defaulting. I'd also take a look at PS request, or PS Pressure switch PID. Hmm, and AC request. For some reason the ECM wants that IAC there.

Do you have an IAC checker? Some noid light kits come with an IAC checker that plugs into the vehicle harness and has a couple LED's to indicate ECM trying to control. I've had a rash of Pickups that had bad connectors and would do as your cavalier is doing at times. Might be worth checking into the connector as well, despite it being a shot in the dark as I dont think I have ever seen an old one like this go bad.

 

[tjthorson]

Yes Todd, just like our Buicks, this could cause a high idle as the ECM is defaulting. I'd also take a look at PS request, or PS Pressure switch PID. Hmm, and AC request. For some reason the ECM wants that IAC there.

Do you have an IAC checker? Some noid light kits come with an IAC checker that plugs into the vehicle harness and has a couple LED's to indicate ECM trying to control. I've had a rash of Pickups that had bad connectors and would do as your cavalier is doing at times. Might be worth checking into the connector as well, despite it being a shot in the dark as I dont think I have ever seen an old one like this go bad.

Thanks. I just ordered a "injector iac noid set", so thats on its way.
For grins, I am going to pick up a tps, MAP, and temp sensor... they should prob be replaced after 24 years.... this thing only has 51000 miles on it - so most if its original. I can tell because that "rusty jones" waxy crap is all over everything under the hood.

 

[John Larkin]

Glory foaming carpet cleaner will help remove that Rusty Jones engine cosmoline. I used it 20 years ago and it really softened it up for final removal but you have to move pretty fast.

 

[gsgns4me]

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?