Light engine popping/backfiring

[240sx_drifter]

So i was driving home from school(I goto UTI) which is about 30 miles highway driving, and about 2 miles city driving, as i got to my exit and was slowing down i noticed that my temp was going up higher as i came to a stop, so i drove around town and the faster i went the cooler it got, so i pulled into my house and filled my radiator with water, noticing it was a little low. it now longer over heats but i have not drove it yet because, this is my main question, only when right before and at op temp and at idle the car has a very light backfire and as you increase the rpm's to about 2k the popping gets semi louder and more frequent. engine also feels like it has a misfire

Vehicle History:
Check engine light on, OBDI, Code 35, Exhaust gas tempature sensor.
Timing is set at 17 Degrees Advance.
I usually run 89 or 91 in it but i put 87 in this morning.(problem didn't start till after drove roughly 50 miles)
Just put in heli coils on 5 out of 8 of the exhaust manifold holes, one is still stripped. the other 2 are fine.

[statickx991]

try replacing the sensor first and see what happens. i take it sr20?

[phaiwezzie]

take the rad cap off and turn on the engine, if it shoots out coolant its a bad headgasket. also check your oil for the milky mixture. is it smoking at all?

[240sx_drifter]

try replacing the sensor first and see what happens. i take it sr20?

it's a ka24e, thought i mentioned it. i think it's just off timed, i mean it's got all of the symptoms of being off timed. i know it didn't burn a valve cause i have no black smoke coming out of the tail pipe.

[240sx_drifter]

take the rad cap off and turn on the engine, if it shoots out coolant its a bad headgasket. also check your oil for the milky mixture. is it smoking at all?

i did that and it shot up like 4 inches but we did the same thing with my friends car and it also shot up, and we know that his doesn't have a blown head gasket. as far as water in the oil, it's not milky at all. and there does not appear to be a lose of coolent after rujnning it for a while, no white or black smoke out of the tail pipe, smells a bit rich which is why i'm leaning towards timing along with the other symptoms. any more imput would be helpful though, thanks.

[240sx_drifter]

so i put the timing at 14degrees and i did a comp test, i got
1 - 150
2 - 150
3 - 150
4 - 120

i dont have a leak down tester so i couldn't tell where it was leaking.
there's no water in my oil and no oil in my coolent.
it only does it at op temp.
i'm gonna try filling it up with 91 and see what happens.