2000 Toyota MR2 - Car starts weak only when it's warm start?


my 2000 Toyota MR2 started to act up a bit lately.

I noticed that the car cranks fine, but turns over very weak. almost seems like it barely starts. this happens ONLY when the car is already warmed up.
This does not happen when car is starting from cold start. Like, starting first time in the morning is fine, but after 10 minutes of driving, then turned off, the subsequent starts are weak as a fart from a butterfly. But it does start, and when it does… it seems to drive okay.

Now, I’ve been hearing it can be leaky fuel injectors, or… Mass Air Flow sensor, … or … bad fuel pressure…(which may be part of leaky injectors?)

any idea? help please!

(see correction below)

Get the battery tested for free at the nearest auto parts store. It’s as good a place to start as any.

I noticed that the car cranks fine, but turns over very weak. almost seems like it barely starts. this happens ONLY when the car is already warmed up.

Your terms are contradicting each other. “Cranks Fine” and “Turns over very weak”. It’s one or the other.

If the engine is turning over weak…then it has NOTHING to do with fuel. It’s in the starting system. And since this is doing it when warm…that tells me it might be the starter.

Need more clarification.

battery is good. new one from 6 months ago…

could be a starter binding up when hot . they sometimes do that when they get old. it almost sounds like the battery is weak and it turns over slowly. when it cools again and the metal contracts, no problem

Could be battery cables and connections. Old corroded connections can have higher resistance when hot.

If “turns over very weak(ly)” means that the starter is turning the engine more slowly, then…NO…this situation has nothing to do with either fuel injectors or the MAF sensor.
If the engine is turning over slowly on “hot” starts, it is much more likely to be the result of a heat-soaked starter motor, or possibly a weak battery.

Can you give us a clearer definition of “turns over very weak(ly)”?


CRANKS FINE… but the VROOoooom… does not happen as well as starting from COLD start

(i thought “turn-over” mean that engine fired up)

allow me to type up the sound effect! LOL

COLD start:

turn the key goes : crank crank crank VROOM!
(starts up fine)

Warm start:
turn the key goes: crank crank crank vvv…v…v…v.v…v…rooooom…
(barely seems to start)

oops, that makes my earlier comment null and void.

yes, cranking and turning over are the same thing.

Try leaving the key in the on position for 5 seconds before trying to start when hot, if it starts right up it would be curious but worth a shot.

Barkydog - thanks! i assume you would want me to wait for the fuel pump to do its job and pressurize system.

I think i tried that before. and does the same thing of not starting well. I can try again.
What would that tell us even with wait of fuel pressure to build up, and not starting strong?

I think you have the same problem I do with my '88 Supra. Starts fine cold, but chugs and lugs when re-started hot. My best guess is the ECU firing the cold-start injector and partly flooding the cylinders. Once the rich charge burns off, the idle smooths out and the engine is fine. But, I don’t think your 2000 has a cold-start injector. But, the ECU could be mistakenly thinking the engine is cold and starting with a too rich mix. A scan tool on your car can read the sensors and see what the ECU sees from the CTS.

Like I said it would be curious, waguess would be a fuel line is too close to a manifold or leaking manifold and super hot gas is not igniting properly, won’t make more guesses till I hear the results. It gets way more compicated after that, but a good mechanic should be able to replicate the problem and solve it.

Barkydog - i just test it out. it does the same thing of not starting strong even after waiting 5ish seconds…

@Hyojiggy: “battery is good. new one from 6 months ago…”

Are you assuming that or did you get it tested?

You’d want to figure out if it is lacking fuel or spark.

A hunch: Heat is causing an electrical component in the ignition to fail: if this car has a distributor, the part that signals when the secondary should fire a spark [they go by various names - pickup coil is one]; if no distributor, then maybe a crank postion sensor.

It has a crank and cam sensor. I was wondering if the temp sensor was outputting wrong. It feeds the MAF, TPS and Vapor Press sensor.

I meant to attach the schematics

shanonia - it’s 1zz-fe motor… i think those have coil packs instead of the distributor cap and rotor and wires. would that work the same method as you described?

Knfenimore - is temp sensor something i can test? or should i just replace the part if it’s cheap?
i’m handy, but i’m no mechanic.