I am using a timing light that has a numbered ****/dial on the back to set the timing on my 86 IROC with the 305 TPI. From what I understand you get the car to operating temperature then turn it off and unplug the EST wire. From there you would hook up the timing light and set the **** on the light to zero. Start the car up and slightly move the distributor until the mark on the balancer lines up to 6 degrees BTDC on the tab. I also understood that if your timing is set to 6 degrees with the light set at zero, if you set the light to 6 degrees your timing mark should go to to zero on the tab. I am able to set the timing to 6 degrees with no issues as long as the gun/light is set to zero, but when I set the gun to 6 degrees my timing mark doesn’t go to zero? It goes to 3 or 4 degrees BTDC and once in a while sporadically advance a degree or two? I am having an issue only at initial cold stars where the car will start right up then the RPMS will dip a little then rise to 1600-1700 RPMS then slowly settle down. During this time I notice that my RPM needle is slightly shaky. Along with this my exhaust has a rich smell. From what I described with the timing could that be the issue? Is that normal for the timing mark not to go to zero with the gun set to six degrees? Thanks in advance

 

Sounds like you’re trying to mask an unknown vacuum leak.

While it’s running it should pull a steady 26 - 29 kpa. Try putting in a testing circuit on a vacuum line and see what you’re pulling. Or you could try a smoke test on the vacuum circuits or isolate each vacuum line/device, grab a vacuum pump and start testing.

 

I agree with you it does seem like a vacuum leak. I did the whole smoke test applying smoke through the vacuum line at the brake booster and nothing also did the whole spray the engine with carb cleaner while its running and nothing no changes???

 

Have you done the typical vacuum leak repair at the heating/cooling selector wheel under the dash?

this is a typical leak that is unassuming.

 

Thank you for the reply. Im familiar with that one had an issue with my GTA and fixed it but unfortunately not the case with my IROC. I am getting a constant hissing sound while the car is running from the rear by the fuel tank but I’m afraid I can’t isolate it and I’m unsure which is the vacuum line that runs to the tank. I know there is that plastic vent valve over the differential that vents fuel vapors. I replaced that with no change??

 

Perhaps it’s your evap canister and/or solenoid valve allowing constant flow which would act like a vacuum leak. Have you isolated that to see if that’s the issue?

 

I have the early third gen charcoal canister with the two valves one attached to the canister and one not. I replaced the one that’s not attached with a new one and ran 12 volts to the solenoid and it was clicking so I’m assuming that’s good. The one on the canister could be bad but you have to replace the entire canister and they’re impossible to find. I really do feel it has something to do with the evaporation system

 

Isolate it by pulling the vacuum line from the throttle bottle and cap the ported vacuum with a rubber cap.

 

So cap the line going from the canister to the throttle body? Cap it on both ends? At the throttle body and at the canister?

 

You got it!

 

Thank u so much I’ll give it a try

 

I unplugged the ported vacuum line from the bottom of the throttle body and capped the little port at the bottom of the throttle body. I then put a plug in the ported vacuum line(I think that’s right?) but sadly no change. I’m at a loss. I know it’s hard to diagnose these cars without live data and I think I’m eventually going to have to take it to a shop but I would love to figure this thing out myself. Would a vacuum leak cause the car to run rich? The exhaust is definitely eye watering!

 

Absolutely. Uncontrolled air into the intake will cause your O2 to sense a lean condition. With a lean condition both your INT and BLM fuel trims will start adjusting by adding more fuel.

 

Thanks for the info. I did a little digging around today and noticed that on a cold start the RPMS go to the right spot about 1200 then shoot up to like 1500 and stay there until they gradually go down to between 900-1000 at idle. I do notice the RPMS slightly bouncing. Once it settles down no hesitation while driving or at stop lights. Plenty of power and the idle is steady. Is it possible that when I did the whole IAC reset and adjusted the throttle screw I set it too high? Will it give these symptoms if the throttle blades are open too much

 

I think I figured it out! Fingers crossed. Like most of these cars over the years someone had messed with the idle stop screw on the throttle body. I was familiar with the whole IAC reset/idle adjustment procedure and have done it in the past but have always relied on the dash tach which although is close….its not accurate enough for the adjustment. I used a digital tachometer/timing light and observed that my timing was spot on but obviously my RPMS were too high. I adjusted it to about 490 RPMS with IAC & EST unplugged along with the car in drive and so far it’s been idling great no fluctuations etc. I’m guessing that with the throttle plates being open more than normal it was allowing too much air into the intake throwing off the fuel/air ratio causing the high idle? Hopefully I can check this issue off the list! Thank you so much for your advice and input. I really appreciate it.