P0171 Or 'please Help Me Keep My Ebay Bargain A Bargain!'

[Jonowe]

I've acquired a very cheap, Japanese build, '99 Yaris 1.0. Sadly it's got issues:

Problem: From cold, the idle becomes rough after about 5 miles and the CEL comes on.The code shown is P0171

Efforts so far:

I've cleaned the MAF sensor. This improved the idle, but the problem remained.

I've replaced the MAF sensor. OEM Denso, £92. Ouch. This greatly improved both the idle and performance through the rev. range.

Unfortunately I still had a very lumpy idle. Checking the vacuum hoses revealed that the hose into the purge valve is very perished. Cutting off the end and bodging a clamp with a cable tie improved the idle a bit.

***My questions are***

Is the vacuum system the sole remaining culprit?

Should all the vacuum hoses all have clamps?

Does anyone have the p/n for a complete set of under bonnet hoses

How do I fix this without buying a complete set of under bonnet hoses*

*assuming a dealership is going to rob me blind

THANK YOU!

[Catlover]

One article I read - fuel filter partially blocked therefore reducing flow of fuel making it too lean. Maybe a cheap fix, or maybe not, but cheap anyway. And of course if you just bought the car maybe its overdue for a service.

[Jonowe]

Thanks Joe. It was serviced 1000 miles ago (confirmed with the servicing garage), but that's certainly a possibility and a cheap option for investigation.

[ToyotaAuris]

Hi I currently have same problem with VW Bora from cold start. Not fixed it since its fine after 10 seconds or less after a rev. Its called the idle control valve sensor (or something similar), try changing that, costs £20 or less.

[Jonowe]

Idle control *should* throw a code.

For others' possible reference, it was a vacuum problem. The rear purge valve hose was utterly worn out. Easy fix, except that it's NLA from Toyota (unless anyone knows different?) so I'm running rather inelegant generic tubing.

[ToyotaAuris]

Idle control *should* throw a code.

For others' possible reference, it was a vacuum problem. The rear purge valve hose was utterly worn out. Easy fix, except that it's NLA from Toyota (unless anyone knows different?) so I'm running rather inelegant generic tubing.

Nice to see you have fixed it but Idle control doesent always. Most of the time it does but on my vehicle it doesent for some reason but agreed it should.