I wish mine looked this clean

My fellow motorist did ask the question. “Fuel economy is why I rev it so!” I did answer. My MR2 likes to idle high (2k rpm or higher) if I don’t give the engine lots of revs, and it’s become worse lately. I’ve signed up for autocross this coming month but I’m not sure how to diagnose/fix the throttle issues.

First throttle issue: doesn’t like to idle.

  • Accelerator pedal feels imprecise compared to other cars I’ve driven.
  • The engine will hold steady at ~2,000 rpm when lifting off throttle in neutral or putting the clutch in to shift.
  • Only remedy is on an immediate basis: hit the gas hard while in neutral and lift just as quickly. Revving the engine makes it drop back to normal idle.
  • This high-idle behavior shows up any time I lift off the gas lightly rather than abruptly.
  • It’s been getting worse lately, sometimes revving higher than 2,000 when I put in the clutch to shift.

I think this issue is entirely related to the accelerator pedal or throttle cable. I can provide pictures of the assembly as it sits in my car currently.

Second throttle issue: hesitation under hard acceleration

  • Sometimes (read: randomly and I see no correlation with any other factor) my car will hesitate intermittently under heavier acceleration.
  • Briefly and repeatedly cuts into throttle output. This shakes the car forward and back due to the rapid changes in the acceleration vector.
  • The revs and road speed remain correlated. No clutch slippage.
  • If the issue manifests itself during a drive, it gradually gets worse, showing up even under lighter acceleration.
  • It goes away entirely if I park the car and start it again later, or if I brake hard and slow down in a straight line.
  • The way the hesitation shows up is different every time. Sometimes it’s choppier and sometimes it has a higher frequency of hesitation.

I’ve researched this issue and it’s probably a fuel pump issue. I’ve never had the fuel tank serviced, nor ever driven it to below a quarter tank in my four months of ownership (the fuel gauge on the dash seems to get sticky below that level and I don’t trust it).

Currently I’m just looking for an accurate diagnosis of these problems so I can begin to go about fixing them. I plan to autocross it again if I can fix it with a few days left before the event, so I can drive it and confirm it’s healthy again before autocrossing it.

Advise me, Oppo... I’ll get to thank you all for some great autocross adventures if I can fix the throttle issues.

Now that that’s out of the way, here’s an update on my friend’s Miata project:

After 2 days worth of effort, we haven’t been able to bolt the downpipe to the exhaust manifold and form a proper seal. There simply isn’t room in the engine bay to turn a wrench for the 3 bolts. We can’t assemble them outside the car and then connect it through the engine bay because the steering column blocks the O2 sensor that’s connected to the downpipe.

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The current plan is to have a local muffler shop assemble it so that it can be smogged and driven. Further wrenching efforts should be easier once the car is assembled properly. I’ll post updates on the project as it develops.