93sprucesc

Hello,

I have a 93 SC300 and I just had the engine rebuilt. Basically overhauled the car. But now when I start my car in the morning it is perfectly fine until 5 minutes later. The idle starts going up and down then after another 5 minutes it goes back to normal. There was a day when my car just did not start til I messed with the intake and the mass air flow sensor. I took it to a place and was told it was the sensor so I replaced the sensor today but the problem is still there. If anyone knows what is wrong with my car please let me know. Thanks!

NaturalJZ

iTrader: (1)

Well i dealt with a bad MAF recently so i'll say to try to find another sc300 that runs, and swap maf to see if thats the problem.

V8drummer

iTrader: (5)

Could be the Throttle position sensor

Tabaka

iTrader: (8)

If it goes up above your normal idle speed, then drops down well below your typical idle speed, and repeats in that scenario than it's most likely your TPS. If it simply falls below your normal idle speed and never raises high, go low, high, go low, and gets dangerously low to the point of stalling, then it's probably your IACV.

Has your car ever thrown a CEL?

Nova

iTrader: (21)

if you do have a CEL on take it to autozone or advanced and they will run it for free and print out possible causes. best place to start instead of throwing parts at it

blacksc4

iTrader: (1)

if its not throwing a cel, i would start with a little cleaning (cheapest possible fix) clean up the TB, and IACV, even possibly sea foam the car if you want, if that doesnt fix it then start going with parts like the tps,

one thing it might also, since you said the engine was rebuilt, who ever rebuilt it, did they tune your tps back to the correct spot? you can try adjusting the tps to level out the idling, it probably idles normal wen start because the engines not as hot, as it heats to running temp, the idle drops so when you adjust it youd be able to have run corrrect, just a thought

there is a DIY on here on how to check the tps for functionality so do that before you buy one, make sure its bad first

Tabaka

iTrader: (8)

if it's OBD1 most of them won't check it

There is a DIY on how to check a code for free along with the code listings in one of our stickies.

OP, try cleaning the throttle body and IACV a little bit and see if that helps.

lexdud

Check the MAF and everything else that others have suggested but also consider the brains ... the ECU. The ECU controls most major engine functions.

93sprucesc

Thanks everyone. I will check those things out and let yall know.

lexdud: The ECU was rebuilt as well

93sprucesc

oh yeah and there is no CEL on

Tabaka

iTrader: (8)

What do you mean by rebuilt? You shipped it away and had capacitors replaced or something?

JDMmuscle

iTrader: (9)

Check all your vacume lines. Mine did the same thing, Bought a new maf, refurbed ECU, TPS, the works.... turned out one of my vacume lines had a small tear in it.

blacksc4

iTrader: (1)

^ to check your vac line run the car and spray a mist of brake cleaner or water and if it sputters then theres a leak in the line

thot id fill in if you didnt know how to check

Nova

iTrader: (21)

your right sorry op I forgot ur car was obd1 when I was writing that post so scratch my other post about autozone

Tabaka

iTrader: (8)

Where are you asking the OP to spray this brake cleaner?