Bala501

Hey guys, normally this is the type of problem i'd try solving on my own. But i'm really at the end of my rope here figuring this out. I have a non VVTI 97 SC300 Pretty much with any cold start, seemingly regardless of weather. My car idles rough, throttle response isn't there. It kind of misfires and isn't as smooth as it usually is (really isn't smooth anyway until i hit like 5,000 RPM then it seems to run awesome). When i i take off down the road accelleration is very jumpy and delayed. If i rev my engine at idle, the rpms drop down to below 500 sometimes and it feels like it's going to stall. But for the most part when it's warm it kind of runs great, minus the engine vibration and lack of smoothness till 5k rpm I can record and upload a video if need be i am just really sick of chasing this issue. This is what i've done so far

So far i've done; plugs, wires, distributor cap & rotor, new throttle position sensor, cleaned my MAF, cleaned throttle body and upper plenum while doing plugs and wires, sprayed ether/solvent out of a can around the mating surfaces on the intake to check for leaks. Brand new fuel filter, fuel pump ECU bypass w/ soldered and heatshrunk connections. ECU repair, double checked and triple checked my joints and i'm positive i replaced all caps including like 2 leaking tantalum ones. Ran a few bottles of injector cleaner, i only use 93 octane from cumberland farms & BP. Tested my ignition coil and im im pretty sure the numbers are within spec. This is driving me crazy, its getting pricey and i needed to do most of these things anyway but im worried about reliability. Any help would be absolutely appreciated, thanks guys.

RudysSC

A few things to try... You may have damaged your MAF by cleaning it - those sensors for these cars do not like to be cleaned and can often times damage the sensor. Also, if the car runs well warmed up, it may be worth replacing your coolant temp sensor to see if that alleviates the issue since it seems to change with engine temperature.

Bala501

Hey Rudy, thanks for the reply & suggestion, i may have got lucky with the MAF. It's my first lexus/toyota and i didnt realize they were designed differently from hot wire ones. Anyways i picked up a new coolant temp sensor and i'm pretty sure it fixed the problem! Out of everything i had done/yet to do, i wouldn't have thought the temp sensor would be it. the plastic plug on the sensor itself was extremely brittle and broke off when i disconnected it from the harness, so it was probably long since due. She runs beautifully now, i appreciate the help

RudysSC

That's great news, glad to be of help! Enjoy that bad boy.

Bala501

Actually it didn't completely solve my issue. I guess next is replacing the maf.

RudysSC

The MAF could certainly be part of your issue especially after being cleaned. Give that a go, and perhaps someone else will chime in if they have any other ideas?

Ali SC3

iTrader: (10)

The 96+ maf is hotwire and you can clean it with regular maf cleaner, you shouldn't have to replace that one just give it another cleaning if you are not sure.
92-95 you do not want to try and clean.

Honestly sounds like the ecu still, I never trust repaired ecu's that much they seem to have issues like that afterwards that are hard to diagnose.
I would see if you can find another 97 ecu to try out and see if that helps. especially if it happens on hot or humid days, that points to the ecu more.

RudysSC

Thanks for clearing that up, Ali!

RXRodger

iTrader: (2)

Yeah still sounds like an ecu issue, that's my first thought. Another thought is since it is temperature responsive, the temp sensor in the MAF may be giving a bad value but I can't decide if that would give the symptoms you describe. You might check the resistance on those two pins on the MAF and check against what the book says it should be. I can't get to my 97 wiring diagram anymore so can't tell you what that should be or what two pins, I know on the earlier MAF's its pin 4 and 5.