Hesitation from start-up

[vrsmxtb]

I'm having some throttle hesitation on a 1.8 mk1.

When first driving off, starting from both cold and warm engine, I get quite bad throttle hesitation / stuttering at lower revs. It goes away after the first few minutes of driving, and also if I give it more throttle it'll suddenly jerk back to normal performance after it hits above around 3k+ revs. The hesitation feels like overfuelling, for example when you run too much manual choke.

Engine was recently changed, and running new leads and plugs.

Could it be the main Idle Air Control valve?

[MX-5 Lazza]

Sounds more like the engine temp sensor on the back of the block.

[gdaybruce]

I have something similar on my 1.8 Eunos, albeit mine is essentially a cold start problem. I recently fitted a new (recon) cylinder head and now if I give it any throttle within a minute or so of starting it up, it just dies but if I let it tick over for a couple of minutes before driving off, it's fine. (Less of a problem in this warmer weather.)

I've replaced the temp sensor at the back of the head with no improvement and the idle air control valve seems to be OK so my main suspect now is the throttle position sensor (TPS). I've just bought a multimeter so that I can test how it's working.

[PATTERNPART]

Mine does it a bit from cold. Low revs trundling up a gentle 30mph urban road. If I try to apply slightly more throttle its as if the brakes are being gently applied. Then it clears.

[lodgey77]

Mine did this, timing was out. Easy fix. Failing that swap you plugs and leads.