Engine revs drop initially when pressing the accelerator

[hambleton1]

Hi All,

I have a 1999 Yaris 1.0L. When the engine is fully warmed up the idle drops to around 500-600 RPM, which is supposed to be normal for the Yaris. 

However, when pressing the accelerator to pull away the engine will almost stall before the revs come up to where they should be. This is particularly bad when needing to pull away quickly because the car won't go for a second or two because the idle drops before rising back again. This doesn't happen when the engine is cold because the idle speed is higher. I hope this makes sense. 

I've also tried blipping the accelerator in neutral, and it does exactly the same thing.

Can anyone help as to what this may be? 

[Madasafish]

Most likely cause is a dirty MAF sensor.. Can be cleaned WITH CARE.

[Theresa Angeletti]

I just bought a 2018 and have less than 1500 miles and mine does that also. I took it to the dealership yesterday- they said no thing on the diagnostics. Nothing they can do. It is scarey when you have to accelerate quickly in traffic or on the freeway. I have no idea what to do next. :0(

[Sala296]

Hi there,

I had the same issue myself. It turned out to be 2 separate but related issues. The first was an air hose underneath the air box had come lose, the clip was missing so I got a jubilee clip from Halfords and popped it back on. The second issue was the MAF sensor, I tried cleaning it, however it didn't help. I replaced it with an aftermarket one from eBay for about £25 (£20 now) and now it drives flawlessly.

Here's the MAF (Make sure it's definitely compatible, PM me if you want me to take a look):

https://www.ebay.co.uk/itm/For-Toyota-Yaris-VITZ-AVENSIS-1-0-1-3-16V-Mass-Air-Flow-Meter-MAF-1999-05-PINS/252692035223?epid=5016650572&hash=item3ad59e7697:g:Z8wAAOSwLF1X~LhT

And the hoses that came loose and may be worthing checking can be found by unclipping the air box (red circles), and looking where the green arrows point:

Good luck, and don't hesitate to get back to me with this 🙂 

Michael.