Hello All,
My 86 c4 base model is driving me crazy, I hope that gets someones attention. The damn thing will not idle correctly after all the stuff that I have done to the beast since I got her back in September of last year.
I have changed the following items:Sorry I dont know all the acronyms, so here we go.
Idle air valve
Water temp sensor (up front next to cold start switch) and new connector
EGR gasket and new connector to EGR vac switch
Spark plugs and new cables
new o2 sensor
MAF Relay and Power Relay (I had a code for the burn off relay)
replaced the distributor cap
Replaced the ESC module and capacitor in the distributor
replaced the fuel injectors
replaced the plenum gaskets and the throttle body gasket
lastly I replaced all or as many vacuum hoses that I could find and get to

yet she still idles erratically, hunting up and down from 6 hundred rpm to 8 hundred rpm.
Other then the idle situation she runs like a raped ape, has god power, especially after I put the new injectors in.
So this is my first Vette, and I'm not totally unfamiliar wit the Chev 350 as i have owned 2 Camaro's one with a regular 350 and the other one was a z28 and 2 firebird's
For all I know this is typical for these cars, or maybe not, really could use some help here

Thanks Everyone


Edit: 2/12/20
Well I found the problem. It turned out to be the base idle and the TPS adjustment which was way off about .35 volt. I was able to adjust the low end to the .54 that it calls for, however the WOT which I read has to be at a min of 4.0 volts was reading 3.79 volts so I may have to replace the TPS soon. Even though the idle is not perfect its a heap better then what it was. Also when I put it into drive it does not chug-gel any more. Very happy at this point.

I want to thank all the member that help on this it was a pleasure.

Tony

 

What exactly did you put in for injectors and where did they come from?

IDK but I believe you can scan the car for live data. Did you? If so, what is the IAC count when the motor is in closed loop? Does the CTS agree with what an IR thermometer would say if it scanned the CTS? Is the IAT reasonably close to what the ECM sees?

 

. Check for a small vacuum leak in all hoses that draw vacuum . Are your codes for a CEL now gone? I have the same problem but mine runs like this when the temp is colder outside.I have it narrowed down to the MAF sensor malfunctioning but mine seems to be weather related . Also I'm going to get a new MAT sensor. Manifold Air Temp. As stated above scan is best. I'll be doing that as well. I had many leaks and slowly got it to run better as I fixed them . My EGR connector was cracked sucking air as well as the small rubber hose that connects the PVC pipe to the manifold. Attachment 48344679

 

I bought OEM Fuel Injectors EV1 GM TPI 22lb/3Bar 5.7L 5.0L 1985-1992 from ebay they were middle of the road injectors as far as price. I could not afford the expensive ones.

As far as your other questions I have no clue as to what your talking about, I dont know all the acronyms yet and I dont have any scanning equipment, and I'm new to the corvettes, so please have patients as I learn about this stuff.
what is a "motor in a closed loop" can I build a scan device that I can use with my laptop, if so how is that done and what software would be needed?
Tony

 

So Tommy, I did as you suggested and I think that there may be a vac leak somewhere in the AC tubes that go into the car. I am having problems with my AC only blowing hot air. I dont know if that's a sign of broken tubes.

Yes, I have no more CEL code. I also should have pointed out that The idle is better after the car warms up fully.

Tony

 

I would get a scanner since it does not just throw a few stupid codes. It gives you an idea of what the ECM actually sees and not just a warning of a sensor reading only if it is out of spec. IOW, if you get a plausible value, no codes although the readings are definitely wrong.

CTS is a Coolant Temp Sensor. IAC is the Idle Air Control. It is a metered air leak to adjust the idle speed.

1320 electronics makes a module that can plug into a port and read data. It sends the data via Bluetooth to your phone.

Closed loop is when the ECM is able to take control and make adjustments to the fuel trim.

 

AC separate issue. I realize you replaced some hoses and gaskets but double check anyway and eliminate it.

Check the rubber hoses that connect to the intake and anywhere a vacuum draws, . A can of carb cleaner with the red straw on the end sprayed carefully at these locations can be use to find a vacuum leak or propane.

Sounds like you replaced everything except MAF. Mass Air Flow sensor. If it starts to fail the idle gets screwy.

 

I prefer to use a scanner. I can get the car to operating temp, see if the IAC counts are 0 and if it isn't, turn the adjusting screw out and rev and recheck. If I turn the screw out all the way and it still doesn't get to 20 counts, I know there is a leak. After setting it to 20-30 counts, I can adjust the Throttle Pos Sensor. I can also check the Coolant Temp Sensor and see what the ECM thinks is happening and hit it with an Infra Red Thermometer to verify. If there is an Intake Air Temp Sensor, I can check it that way for accuracy. After all is said and done, adjust the TPS.

 

Sometimes when an engine hunts at idle it is because it’s too lean. I’m not that familiar with the throttle body on an 86 but i think you can adjust the throttle blade to adjust the idle to its correct setting the procedure should be in the FSM. You could try adjusting , probably closing it more and let the IAC valve do it’s job.

Oh if you do that I’m sure you will have to adjust the TPS as well, which also will be in the FSM.

 

The IAC will do it's job assuming it is working. It will try to achieve the commanded idle. You can't adjust it in and out "***** nilly". This ain't your Daddy's carbed car.

 

that’s my point adjust the throttle/idle as per the book and the IAC will work properly and do it’s job. But you’re right people do fiddle this these cars without following the correct procedure and get undesirable results like a hunting idle condition as the ECM chases it’s tail.

 

I don't like the FSM process. It would work ONLY IF everything but the idle was right. If your tach is out, which it is often, if your sensors are not right, etc, the procedure does not work

 

Andrew, I wanted to send a post to you directly as you seem to know all about how to use a scanner. Well I sent the Red Devil River scan tool that I purchased off eBay back, in my opinion it was a total piece of crap. I went ahead and purchased a 1320 electronics 12 pin scanner. It's not the Bluetooth variety but just the standard USB type. So now that I have the proper equipment to test my 86 C4 if you would not mind I would like to pick your brain and ask you first off if you know what file I might need to select from 1320 electronics that will work on my 86 C4. The last time I looked simply for the L 98 engine but did not find one specific to a 1986. If you have some insight there Andrew I would appreciate it. Secondly should I do my initial scanning on a cold engine or a warm engine or does it really make a difference?
I still have a very erratic idle and I do believe it may have something to do with my IAC. I made a very big mistake when I purchased the replacement one not noticing what type of pintle it had on the end, so I'm not sure if I have the right one in there, and I also did not know they were adjustable, exactly how is that done? I went and purchased a new TPS figuring that the last one was 30 some odd years old and every time I tried to set it according to the procedure with a volt ohm meter the TPS kept throwing a code 22 at me. The only way I was able to get rid of it was to re-install the old. one. Might you have an idea as to why that was happening.
I guess that's all for now, Unless there is any particular way I need to set up my new scanner. I went and printed out all the instructions and I'm going to go ahead and use it with ALDL Droid as well as with tuner Pro which I've already downloaded and installed on my laptop. As usual any help you can offer will be great, I really appreciate it. Hopefully I can finally get my Corvette running really nice and BTW I have learned most of the acronyms so I can probably understand anything you might say.

Tony

 

Hey Tony, did you ever figure out a solution to your issues? It appears you were experiencing the same exact conditions I am currently experiencing and would love some insight into how I may fix it!