Thread: Help! rough idle then stall.

Ok after two days of installing my top swap i am left with a problem:
Initial start up went fine it appeared. rand for about 1 min with no problems. I turned it off. Checked for leaks. All was good. Second start up went well and lasted about 2-3 min. Third start up I planned to take it around the block. I only made it about 500 feet and the idle started pulsing. Adding gas didn't help, it stalled out. I looked it all over and everything seemed fine. I figure vac leak. After letting it sit for 5 min I got it started and back to the house by keeping the rpm's up. I couldn't get it up the driveway as under load it stalled. I let it sit over night and next morning I got it up the driveway just as it stalled again.

Today I have done the following:
*Fuel Pressure Check. would shoot to 55-60 and then fall rapidly.--> bad FPR swapped with L36 as they are the same.
*Compression Check: all read 180 psi.
*Spark Plugs: All looked normal no oil or water. Checked coils and were good.
*Check exhaust and tightened clamps on headers
*RTV's SC gasket, zip-tied all the vac lines, swap PCV from the know good one that came off the L36.
*Re-torqued SC.

After rechecking everything I started it up and after only 45 seconds, same thing happened. Pulsing idle and then stall. ONLY this time I see coolant from the LIM on driver side rear. So my guess is LIM is leaking when it starts getting warm. When I installed the LIM gaskets, Al ones from ZZP, I used a dab of red RTV on the corners and red RTV on the bolts but not a bunch. Also, from the Data log the O2's are not moving. On start up they are in the 800-900 then fall to 50's and stay there. Is is it possible my O2 died? As it was working on before the topswap.

I have video, pictures, and screen shot of data just as it dies. any help or suggestions would be appreciated.

i hate to even ask this one, but have you double checked the plug wires?

Plug wires are fine. Double any tripple checked and when cold it runs fine. It has to be the lim gasket. It's the only hung that makes any sense to me. As it warms up coolant starts to leak and let air in. I picked up another set of metal LIM gaskets, oil, and will rent a coolant psi tester tomorrow. Time for day four!

id pressure test before tearing it apart.

Sounds similar to when my car blew the boost gauge line off down by the firewall. vacuum leak like crazy. my MAP was at like 95 all the time though

Well there is deff a leak of coolant. It is right at the seal between the LIM head and block. Today I redid everything from the sc gasket up and still same issue. I'm almost tempted to redo the head gaskets too! But the compression tests are great so as long as the coolant ports aren't leaking I'm good. But I don't think it would leak where I see coolant if that part of the head gasket was leaking. Also that wouldn't cause my stalling issue as I have good compression. I'm gonna reread the how to for a LIM anyone have a link to a really good one?

is your coolant leak anywhere near the heater hose coolant elbows?

unless your coolant ports are sealed of that idea wont work, the sc would need to be on when pressure testing.

i cant read today apparently. rock on lol

Did you add a good amounts of RTV on all corners of the LIM. Bottom of it.

I only used a little... Maybe I needed more?

I usually add a good amount all across the where the front and rear gasket go on the block on the bottom and top for a good seal, and a good amount on the corners. Done plenty and never had issues.

i dab rtv on the bare metal between the block and heads, (corners) then put the gaskets in. the rubbers ends and the lim gaskets, then one more dab in each corner. then put the lim on.

Got it running!!! My buddy Mike came over gave me a hand and helped bounce ideas around.I can't say for certine what the solution was. Here is everything I did:-Replaced SC gasket-tightened the TB more but was pretty tight-fixed coolant leak. The port on the LIM wasn't tight and was leaking.-I did not redo the LIM as I was pretty sure they sealed good and I did use rtv where the two gaskets met.-coolant psi check. Held 17psi for 45 min-swapped the mini harness for the icm and crank sensor to my old one. I had swapped these as I hd a spare that I wrapped an cleaned up. I decided to run as many known good parts from the L36 NA setup I could.bottom line... It fired up and stayed running. Took it for a spin around the block and checked for leaks. All is great! Now the fun begins... Tuning it.

good to hear.