Can't get rid of this hiccup /stumble / missfire??

[ram_man]

I believe I made a thread awhile back about thos. My 02 saturn when cold first start of the day within the first mile of leaving it'll give you one violent buck. And then it's fine for the rest of the day. Didn't do it for almost a month and then did it 2 times in two days. ..I've changed plugs wires diverter valve map iats checked injector and coil resistance.
Everything just seems fine. No engine codes.....what else can I check?

 

[Gokhan]

Malfunctions that depend on engine temperature are virtually always related to something in the fuel or emissions systems that's supposed to kick in at a certain temperature. Find a repair manual and go through the list of the components in the fuel system and emission system that have any temperature dependence and then go from there.

 

[artificialist]

Do you know when your coolant temperature sensor was replaced? They frequently fail on Saturn 1.9 SOHC and DOHC engines.

 

[ram_man]

Temp sensor is a brass sensor not the plastic and resistance checks out .

 

[old1]

had a 1 year old Grand Am back in 98, that acted verry similar to what you are describing. Was still under warranty so took it to local dealer, and after 3 tries, they replaced the oxy sensor, and never a problem again.

 

[ram_man]

Which oxygen sensor upstream or down. Upstream was replaced.

 

[Warstud]

Are you saying it didn't stumble for a month after you replaced those parts?

 

[ram_man]

Right. But it's never been consistent sometimes it would do it 3 days in a row and then not do it for 5 days then do it 2 times in a week. and we had some warmer mornings last couple mornings had been cooler. And cooler mornings seems to be when it does it most often .

 

[anonobomber]

The upstream sensor is going to be used to modify fuel/air ratios by the ECU. The downstream is only used to measure the effectiveness of the catalyst.

 

[ram_man]

Kinda what I was thinking my upstream was replaced and verified its performance.

 

[Maritime Storm]

Are using stock NGK copper/nickel plugs? If not, you most likely have the answer to your problem.