# Older Sienna's chugging, then acclerating; mechanics baffled

**URL:** <https://community.cartalk.com/t/older-siennas-chugging-then-acclerating-mechanics-baffled/74908>\
**Category:** Maintenance/Repairs\
**Tags:** sienna, toyota\
**Created:** [October 10, 2012, 7:17am UTC](https://community.cartalk.com/t/older-siennas-chugging-then-acclerating-mechanics-baffled/74908 "2012-10-10T07:17:49Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![macwacks](https://avatars.discourse-cdn.com/v4/letter/m/76d3ee/32.png) [@macwacks](https://community.cartalk.com/u/macwacks)\
**Post date:** [October 10, 2012, 7:17am UTC](https://community.cartalk.com/t/older-siennas-chugging-then-acclerating-mechanics-baffled/74908/1 "2012-10-10T07:17:49Z")

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I’ve spent a lot of $$ trying to fix a persistent problem on my 2000 Toyota Sienna CE van. Engine chugs at idle & low speeds, then accelerates suddenly (when rolling, in gear). Have tried: changing timing belt (+ water pump), cleaned fuel injectors, replaced all of these: crank sensor, fuel filter, spark plugs & wires, ignition coils. $1800 later, nothing has worked. My usually spot-on small-shop mechanics (2 different shops) are baffled. It still (sorta) runs, but the sudden acceleration is a hazard in traffic & it’s not reliable–maybe not even safe anymore.

Local shop ran full diagnostics at our expense. Code results: PO 301, PO303, PO305, PO1717, PO171, P0172, P1130, P1150. Translation: Cyl.s #1,3,5 misfiring. Fuel trim lean, bank 1; rich bank 2. (This prior to sparks & wires replacement.) They recommended replacing both A/F ratio sensors, which would run another $700 (at their shop, book rate). Did not authorize repairs, as I don’t trust this shop & my other mechanics doubted this was THE cause of this problem. Reluctant to spend another $700 if that repair is not likely to resolve this issue. Any ideas?

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**Author:** ![bennyandthejets](https://avatars.discourse-cdn.com/v4/letter/b/b487fb/32.png) [@bennyandthejets](https://community.cartalk.com/u/bennyandthejets)\
**Post date:** [October 10, 2012, 2:58pm UTC](https://community.cartalk.com/t/older-siennas-chugging-then-acclerating-mechanics-baffled/74908/2 "2012-10-10T14:58:26Z")

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Clean MAF, clean or replace the IAC and check the TPS for electrical flat spots or less than smooth resistance increase with VOM

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**Author:** ![macwacks](https://avatars.discourse-cdn.com/v4/letter/m/76d3ee/32.png) [@macwacks](https://community.cartalk.com/u/macwacks)\
**Post date:** [October 11, 2012, 1:34am UTC](https://community.cartalk.com/t/older-siennas-chugging-then-acclerating-mechanics-baffled/74908/3 "2012-10-11T01:34:36Z")

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Thanks, Benny. But please, could you translate the acronyms? I have no idea what those initials stand for. (I’m not a technician, just the car’s owner & not very literate about such things.)