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It’s about 25 degrees outside and I hadn’t started my stock ‘85 L98 in couple days. I go to turn it over. Fires right up and then dies! Turned it over again same thing. Second time I gave it a little throttle for about 5 seconds, but as soon as I let off it shuts off.
I look underneath on the floor and see a puddle of coolant right under where the C4 Vette logo is on the driver side valve cover. I grab a flashlight and see that the coolant has collected where a coolant hose connects to a metal flange right under throttle cable (bare with me I’ve got photos).Not sure how the coolant collected there and ended up closer to the firewall and dripped on the floor, but I’m sure you can all answer that.
Last edited by Jordan Little; Jan 4, 2018 at 08:03 PM.
Reason: Accidentally Posted Before Finishing
My first thought is a stuck shut IACV. If you keep slight pressure on the accelerator does it keep running?
Coolant may be unrelated. Looks like there is a leak at the thermostat outlet hose and it's running down the bottom of the housing.
Yeah, if I have my foot on the accelerator and it’s above idle rpm it will keep running, but as soon as you let off it cuts off. I figured the coolant is probably unrelated I just found it weird for them both to occur at the same time. I haven’t had the car too long and I’ve never tried to fire it over in this cold of weather. Thanks for all your useful information!
Another vote to check the IAC. Had intermittent issues with my 86. When it was cold out, start and run for a few block then around 165 degrees ran like crap and barely able to keep running, definitely had to keep feathering the accelerator to get it home. Let it set about 30 min and it ran fine. Kept coming back to the IAC, one day gave it a few raps (not hard but enough to shake it up a little) with a plastic faced hammer. Evened out and hasn't given a problem since. I think it was sticking when it was cold out and that shook it loose.
Another vote to check the IAC. Had intermittent issues with my 86. When it was cold out, start and run for a few block then around 165 degrees ran like crap and barely able to keep running, definitely had to keep feathering the accelerator to get it home. Let it set about 30 min and it ran fine. Kept coming back to the IAC, one day gave it a few raps (not hard but enough to shake it up a little) with a plastic faced hammer. Evened out and hasn't given a problem since. I think it was sticking when it was cold out and that shook it loose.
Just a thought.
Just take the Jeremy Clarkson approach with a hammer? Haha if it worked for you it’s definitely worth a try. Thanks for your input.
You should get a reading on what the fuel pressure is first.
Do you hear the 2 second prime for the fuel pump when the key is turned to the ON position?
Start with the Fuel pressure as a Known, Try to get a Fuel sample check to for Water. Clean the Throttle plates then as suggested give the IAC a look at.
As for your Coolant leak I think you may Have a Pretty good Intake Leak, Clean up the coolant Check Hoses/Clamps & Thermostat Neck and Gasket Run or Pressurize. But I will bet you will see the Intake bolts getting wet or a line of coolant form on to edge of Intake
I figured the coolant is probably unrelated I just found it weird for them both to occur at the same time. I haven’t had the car too long and I’ve never tried to fire it over in this cold of weather.
I find that cars get stupid in the cold. Weird stuff just happens.
As stated about your IAC is faulty. Replace it or wait for warmer weather.
Your thermostat gasket is shot. Need to replace it as it shrunk in the cold.
Now, here is your Three-peat; Take off your Throttle body and you will accomplish the following:
1) clean the TB for better performance
2) easier to change out your IAC
3) easier to change your thermostat
It’s about 25 degrees outside and I hadn’t started my stock ‘85 L98 in couple days. I go to turn it over. Fires right up and then dies! Turned it over again same thing. Second time I gave it a little throttle for about 5 seconds, but as soon as I let off it shuts off.[left]
In reviewing again, if you can get it to run for 30 seconds with your foot on the accelerator, chances are the fuel pump and pressure is OK and I would focus on the IAC. Stated in post 2.
I would also clean up all coolant before starting in the event it might be sucked in thru the manifold or whatever and mix with the fuel.
Check for any broken hoses and if you had a radiator pressure tester, that would be a good way to find a leak.
I agree with the suggestions above. Could be a fuel restriction too depending on how much crud you have in the tank. I had another classic car barely run due to blockage in the fuel filter.
On the coolant leak, hope that it is your thermostat gasket as that is a 20 minute fix. My bet is your intake manifold is shot as that area is prone to failure given the "wet" manifold of the L98 (mine did the same). Should be easy to tell if you clean that area and just watch. Lots of good threads on intake manifold replacement here... was a lengthy project for me (but I am slow).
Re: coolant leak - might be worthwhile to remove the air duct off the throttle body and inspect that "U" shaped hose the directs coolant from TB to the block. My '91 was leaking there - ever so slightly though in my case. Took me a while to find it too. I had to put a mirror under the hose to see it was wet. Based on the pooling seen in your pics, I doubt yours is just seeping though - but under pressure maybe its spraying coolant back toward the thermostat and pooling up there ? Just a thought. If it turns out that hose is at fault, its a good time for the TB bypass.
My first thought is a stuck shut IACV. If you keep slight pressure on the accelerator does it keep running?
Coolant may be unrelated. Looks like there is a leak at the thermostat outlet hose and it's running down the bottom of the housing.
My 85 had the same symptoms and it was IAC related. You also have a thermostat housing leak; completely unrelated to your idle issue.
Having said that I also agree that you might want to check the fuel pressure as others mentioned. Is the battery holding a charge? I ask that related to the alternator being that it is 33 years old if original. I had to replace mine as well. Good luck!
Help Me Figure Out What’s Wrong This Time
Start with the Fuel pressure as a Known, Try to get a Fuel sample check to for Water. Clean the Throttle plates then as suggested give the IAC a look at.
