I got the car back with the new IACV put in (paid $75 for the labor), but it’s still having idle issues. The rising idle issue is still present, but at least now it is intermittent.
Bob at Sunland Auto thinks that it could be an issue with the MR2 ECU (P/N 89661-17020) not talking correctly with the Corolla 4AGE that it’s connected to, and that maybe we should swap the ECU with one for a Corolla.
After doing some research, I found that the ECU on an American Corolla (P/N 89550-12720) does not match the ports on an MR2’s wiring harness. However, the ECU on the Japanese Corolla Levin/Trueno/AE86 (P/N 89661-12051) is a 100% match for the pins on the MR2 harness. But for now I’ve decided to wait on ordering an AE86 ECU from Japan until I rule out the other common issues.
From what I could find, the rising idle is likely caused by one or more of the following:
- Coolant needing to be bled properly
- Vacuum leaks (idle-up VSV, vacuum lines in general, etc.)
- Cracks in the intake after the AFM but before the engine (intake tubing, throttle body, intake manifold, TVIS, etc.)
- Bad AFM, TPS, IACV, or ECU
- Dirty throttle body and intake manifold
Since I’ve already had the AFM, TPS, and IACV replaced I ruled them out for the time being. The coolant will need to be bled properly again, but I need to review the process and do it myself when I get time. Vacuum leaks have been all fixed according to my mechanic, but there was mention of a VSV being bad. Since I had never taken apart this car beyond just the air filter housing, I decided to get up to the throttle body and clean what I could.
I forgot to take pictures before I got started, but here is what the throttle body looked like after I cleaned it up and flushed out the PCV and vacuum lines on it with carb cleaner:
I did take a picture of the intake manifold before I got started, and this is pretty much what the back side of the throttle body and the inside of the PCV and idle stop screw looked like:
I tried cleaning into the intake manifold as much as I could, but even a long pipe-cleaner like brush I had could only get so far. One day I’ll order some gaskets for the intake manifold and TVIS and clean out the entire thing properly.
This helped with the idle issues once I got the engine fired back up. The idle was able to be adjusted with the idle screw on the throttle body, and I was able to get it to a consistent 1K RPM at normal operating temperature. However, it didn’t last long — the rising idle issue came back, but it started stopping around 1400 RPM instead of going all the way up to 1600 RPM and causing the ECU to cut the fuel injectors.
All was not lost though, I learned a heck of a lot about the intake of this car in the process, and I found the following issues:
- The throttle body linkage was missing a spring that helps close the throttle plate when the accelerator pedal is released.
- The IACV is missing a VTV (vacuum transmit valve).
- The idle-up VSV (vacuum switch valve) has exposed wires and appears to be inoperable.
To remedy these issues I purchased a new spring for the throttle linkage at Lowe’s for about $5. Here’s the before and after:
I ordered a new VTV valve for the IACV from Toyota for $40 (P/N 90925-01014). Here’s a comparison of what my IACV looks like, versus what it should look like with the VTV on it:
I ordered a used idle-up VSV from eBay for $20 (P/N 89570-16080). Here’s what mine looks like currently:
So once the new VTV and the “newer” idle-up VSV get here I’ll be putting them in to see if it helps with the idle.
In the meantime, I decided to move onto the interior LED project and have put in the under dash light strips:
The lights are wired up to the wiring harness behind the climate control panel. In fact, the wires are plugged directly into the connector for the cigarette lighter’s light — which allows the lights to come on whenever the dash lights are turned on.
I almost forgot to mention, while I was working on cleaning the intake I tried to replace the old fuses in the No. 2 junction box (driver’s side engine bay). Here’s how bad they looked before I got started:
I managed to get the 50 amp (red) one replaced by simply pulling it out and popping the new one in. But the 60 amp (yellow) one was stuck in there tighter than a drum… I couldn’t get it out, and nearly broke it trying to take it out with pliers. From what I could find, that fuse may be held in place by a screw that you need to take the entire junction box out to get to (which sort of defeats the purpose of it being a fuse in the first place, but that’s just my opinion). So for now I’m going to wait until I find the motivation to change it out.
For reference, here is a picture of the fuses I purchased:
Tonight I started on painting the trunk with rust converter, and I will post the progress when it is dried tomorrow.