Piston Slap: According to the Throttle Position Sensor…

Sajeev Mehta
by Sajeev Mehta
piston slap according to the throttle position sensor 8230
Brian writes:


This is a weird one, but I figured you would enjoy it. I have owned an ’88 Accord LX-i five speed hatch for a while. One day, driving along, I noticed that it seemed to be coasting easier than normal. When I approached a red light, I found out why: 3,000 rpm was my new idle speed. I stopped, and before I could even think of why this was happening, the idle returned to normal. Once underway, 3,000 rpm was again the new idle speed. Subsequently, I tried many things. This is not related to the brakes, not related to the throttle input, not related to absolutely anything other then wheel speed. In the most stark example, idling on a slight incline, I can just release the parking brake and, once rolling, the idle jumps to 3,000 rpm. Using only the parking brake to stop once again, the idle returns to normal. No CELs or anything else strange happens during this.

I found that it would idle normally if I disconnected the IACV. This worked fine, but when using the A/C it can no longer compensate, so that was not ideal. I also could make it work if I disconnected the speedometer cable, so I did that for a while before really missing my speedometer and cruise control. I tried another way, which was to disconnect the electrical connections between the speedometer and the rest of the gauge cluster. This works, but I get no cruise control, and a CEL only if I coast with no throttle input for too long, which is strange.

I have tried bleeding the IACV, replacing the IACV, replacing and adjusting the throttle position sensor, replacing the entire gauge cluster (which had the same issue, but seemed to change the high idle RPM weirdly enough, but still wonky-high). Also, I did check all grounds and the solder joints in the ECU.

Here is my long standing build/upkeep thread, and here is a terrible video.

Sajeev answers:

Damn son, your comprehensive diagnosis/repairs make it tough to wave my magic wand and proclaim a resolution! But I bet you either:

  1. Tragically bought a defective throttle position sensor (TPS).
  2. Didn’t adjust said TPS correctly.

Your symptoms remind me of a looney month with a 1987 Mustang GT convertible where everyone thought I was rearin’ for a race: whenever I engaged the clutch/popped it out of gear (after warming up) the 5.0 would rev around 4,000 rpm. No check engine light, no joy when swapping the IAC (IACV in Honda-speak), but it fixed itself after swapping a working TPS.

While it appears that installation on your Accord is harder ( video NSFW-ish), while there’s plenty of digital ink’s spilled over Honda TPS tuning and while I’d never doubt your skills…do re-check your work on the throttle position sensor.

What are we missing? Tell us, Best and Brightest!

[Image: OP/Grassroots Motorsports]

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4 of 32 comments
  • Maryland1966 Maryland1966 on Feb 04, 2019

    I also have no clue same as the two guys above. Not sure why I posted but wanted to note that I like the color of this vehicle.

  • ToolGuy ToolGuy on Mar 09, 2019

    Brian/Tuna, Are you still working this problem?

    • See 1 previous
    • ToolGuy ToolGuy on Mar 10, 2019

      Also curious after scanning again through some of the suggestions - have you ever done a dry/wet compression test? (Extremely helpful for peace of mind and ruling out a bunch of stuff.)

  • Art Vandelay I always liked those last FWD 300's. Been ages since I've seen one on the road though. Lots of time in the RWD ones as rentals. No complaints whatsoever.
  • Cardave5150 I've had 2 different 300's - an '08 300SRT and an '18 300C. Loved them both a LOT, although, by the time I had the second one, I wasn't altogether thrilled with the image of 300's out on the street, as projected by the 3rd or 4th buyers of the cars.I always thought that the car looked a little stubby behind the rear wheels - something that an extra 3-4" in the trunk area would have greatly helped.When the 300 was first launched, there were invitation-only meet-and-greets at the dealerships, reminding me of the old days when new model-year launches were HUGE. At my local dealer, they were all in formalwear (tuxes and elegant dresses) with a nice spread of food. They gave out crystal medallions of the 300 in a sweet little velvet box (I've got mine around the house somewhere). I talked to a sales guy for about 5 minutes before I asked if we could take one of the cars out (a 300C with the 5.7 Hemi). He acted like he'd been waiting all evening for someone to ask that - we jumped in the car and went out - that thing, for the time, seemed to fly.Corey - when it comes time for it, don't forget to mention the slightly-stretched wheelbase 300 (I think it was the 300L??). I've never found one for sale (not that I've looked THAT hard), as they only built them for a couple of years.
  • Jkross22 "I’m doing more for the planet by continuing to drive my vehicle than buying a new one for strictly frivolous reasons."It's not possible to repeat this too much.
  • Jeff S Got to give credit to Chrysler for putting the 300 as a rear wheel drive back on the market. This will be a future classic.
  • Lou_BC How to Fix Auto Media? Stop fixating on soft touch plastics and infotainment systems. I did quite a bit of research on my ZR2. There was no mention of the complexity of putting the transfer case into neutral. (9 step process). They didn't talk about how the exhaust brake works with tow/haul mode. No mention that the exhaust brake does not work with off-road mode. Nannies only stay turned off with the lockers engaged. Only one review mentioned the tail pipe as a vulnerability.