rough idle after start up


Well-Known Member
Quick synapsis, helping a friend get his low mileage GN back on the road after a few years. Oil is fresh, primed it before trying to start, added fresh gas, changed fuel filter, checked all the readings on the scanmaster. The car will start up and idle very smooth and sound great but after 30 sec it will stumble and cough. You can keep it running but it wont stay on its on. Smells rich as well. No fuel gauge yet, we are putting a temp one on to check the FP. Anyone have any other ideas for us to check out? Thanks
I would replace the injectors. The new modern ones have excellent idle quality and resist fouling better than those Bosch pintle units.
Could be a MAF issue. You should read 5-6 grams per second of airflow at an idle on a stock car when it's warmed up. While the car is idling well tap the MAF with the end of a screwdriver and see what happens. If the idle goes haywire you have your culprit. If you're watching the scan master you'll see the airflow jump all over the place too.

Might be his fuel pump on its way out when it gets hot .also i know you said fresh gas but what was the color of the gas that was in there contaminated? That would clog the pump .filter. Injecters.would start at the tank .make sure you have real fresh gas .

please see the discussion started by Buickin87. Could be the corrored ECM and chip connectors/pins, you can´t see the slight corrosion. The advices I got in this forum helped me. Pull out ECM cables and chip and put them back and use, if needed, the electronic cleaner spray very carefully to the connectors/pins according to the instructions in the cleaner spraybottle.


The little gas that was in it was in good visual shape. Changed the fuel filter already. Added some fresh gas. Car will it run til it gets warmed up, runs clean and smooth for about 30 sec that chugs and wants to die, the running smooth makes me think its not an injector issue. IAC was high, doing the best i can to get the numbers down low. Fuel reg is missing the lock nut, so we ordered a rail gauge to verify the pressure, smells rich when running. The car has been garage kept so i dont think its a corrosion issue but will definitely check it. Thanks for all the input guys.
So problem was found. Bad fuel line between the pump and the hanger. Never saw one do what this one did but glad it was found and now its on to the next thing.
It was deteriorated thru the first layer of rubber, the mesh middle part was almost gone and the inner layer was thin and ripped so fuel was just being pumped back into the tank.