Weird hesitation on acceleration & rough idle - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 6 Old 06-07-2019, 07:46 PM Thread Starter
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Weird hesitation on acceleration & rough idle

Been chasing this one for a while, really not sure anymore what it is. My truck is a 96 T100 with 246000 miles (rebuilt motor at 175000) and just last week I've started getting a hard hesitation around 3000 rpm when accelerating hard. Basically the truck loses power for just a second then it comes back, making a very noticeable hard jerking. Also, the idle seems to be worse then usual, it starts up fine but once warmed up the idle will dance around from real low like 300 up to 1200 rpm randomly. Pulled codes and got a P0171 system too lean bank one. Checked for vacuum leaks and found none. Past few months replaced O2 sensor with denso part, replaced air filter, cleaned throttle body, replaced TPS, checked wiring for cuts and loose wires, and found nothing out of the ordinary. Hope someone can shed some light on this One. Thanks!
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post #2 of 6 Old 06-07-2019, 11:21 PM
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When you cleaned the throttle body, did you remove it from the air plenum to perform the cleaning? Did you inspect/clean the idle air control (IAC) valve? How did you clean the IAC? Did you make sure the shutter valve opened/closed without any sticking/crunchies?

When you replaced the TPS, did you use an OEM or aftermarket part?

Have you inspected/cleaned the mass air flow (MAF) sensor?

Do you have an OBDII scanner/reader that has graphing/live data capture? If you don't, you should really invest in one as it can make a big difference in performing diagnostics.

P0171 is usually a vacuum leak. Just because you haven't found the cause of the extra air into the system doesn't mean it hasn't gone away.

Have you inspected/replaced the fuel filter? Have you tested the fuel pressure?

1998 T-100 SR5 2WD auto, Roadmaster Active suspension, dual oil catch jars, AC mod, aero cap, lower aero package, 67% grill block, aero single wheel trailer
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post #3 of 6 Old 06-08-2019, 11:39 AM Thread Starter
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Thanks for the tips bam, I replaced the fuel filter 3 months ago, and fuel pump last year. TPS is aftermarket, standard T series part. My scanner has a live data view and I used it to check the TPS. No throttle it reads 5% and full throttle it reads 64% which is weird but I heard that's normal. Long term fuel trim is +2% which isn't that bad. I checked the iac valve a while back but definitely going to check and clean it again. I didn't remove the TB from the plenum when I cleaned it. Also will check fuel filter.
🙂
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post #4 of 6 Old 06-08-2019, 01:41 PM
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Quote:
Originally Posted by julian90090 View Post
Thanks for the tips bam, I replaced the fuel filter 3 months ago, and fuel pump last year. TPS is aftermarket, standard T series part. My scanner has a live data view and I used it to check the TPS. No throttle it reads 5% and full throttle it reads 64% which is weird but I heard that's normal. Long term fuel trim is +2% which isn't that bad. I checked the iac valve a while back but definitely going to check and clean it again. I didn't remove the TB from the plenum when I cleaned it. Also will check fuel filter.
🙂
TPS sounds tempermental.
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post #5 of 6 Old 06-08-2019, 07:32 PM
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I just checked my TPS (key on/engine off) with my Ultragauge and it reads 11% and 74.9% respectively. Engine at operating temp and running, the TPS reads 9.7%. I initially replaced my TPS with an aftermarket one from Rock Auto about 6 years ago and it gave up the ghost about 3 years in. I installed a new OEM that I got off of eBay and haven't had any issues since.

P0120 was the code.
https://www.toyotanation.com/forum/6...lfunction.html

Here's a quick listing on eBay on the TPS units. Some are aftermarket while others are touting to be OEM.
https://www.ebay.com/sch/i.html?_fro...acat=0&_sop=15

You'll want to use yer eyeballs to check all yer vacuum hoses. The one you can't normally git to is the one that "Y's" off of the IAC valve to the intake manifold. Yer gonna have to take the air plenum off to inspect that one. You'd probably want to use propane or brake cleaner to check and see if the engine surges during the test.

1998 T-100 SR5 2WD auto, Roadmaster Active suspension, dual oil catch jars, AC mod, aero cap, lower aero package, 67% grill block, aero single wheel trailer

Last edited by BamZipPow; 06-08-2019 at 10:46 PM.
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post #6 of 6 Old 06-12-2019, 08:12 AM Thread Starter
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Thanks for the info. Going to replace tps sensor and vacuum switching valve which was caked with carbon crap when I inspected it.
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