89 7mgte Rough Idle: a short story of what I have done that hasn't fixed it.

[jfree91]

Bought my car from a single owner 4 months ago. Bone Stock from what I could tell. Would shut off at idle.

I change spark plugs, plug wires, and coil pack. no improvement. I change the MAF/AMF (whichever it is), no improvement. I hear hissing so I try to fix any vacuum leaks, in the process breaking the BVSV plastic nipple.

Not having much mechanic experience aside from regular oil changes and similar tasks, I brought it in to multiple places. First guy tells me he wants to raise the idle and said he needed to drill into the engine block to do so... too fishy so I left. Next guy shorts the vacuum lines between the power steering because it was leaking. no real change other than the hissing stops. After these, I decided to find a Japanese mechanic place to see if the skill is any better.

Next guy is at Nishikawa Auto Service and helped a lot, noticed the CPS had an oil leak so he takes it out and gives it to me to send for a rebuild (thanks @Piratetip for the assist on this). Car now was able to stay on at idle but still stumbled. In the meantime, I had Nishikawa take out the power steering pump so I could go get that rebuilt at CJ Automotive on Firestone in South Gate, CA (cleaned everything, new seals, fresh bead blast, thing looks like they gave me a new one, no leaks, highly recommend.) They put in the rebuilt PS Pump and get rid of the vacuum short. Stumble still exists so I am convinced its a timing issue with the notches on the CPS potentially not matching at TDC. Give Nishikawa a new timing belt, tensioner, and water pump to put in. STILL rough after probably 3k in repair costs (parts and labor). Now I'm pretty broke lol.

• Take it home, save and research more. TPS maybe? I go and check it, while I am there i get brave and take the fuel rail out.
• TPS is super finicky. Like a hair of a turn and it goes from infinite to 6 ohms. Seemed like it might be it, so I buy a new one on rock auto and calibrate. New one isn't as finicky. Get all the requirements down perfect. and tighten.
  Fuel rail is out and covered in carbon. Carb cleaner and take the injectors off. Replaced all seals and filters. Also noticed this little guy.

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• Its all dinged up. Look for a new 440cc injector after asking a rebuild shop. (They tell me this type of injector can get rebuilt but not the part that is dinged up. precision angle holes and spherical surface means need a new on and cant resurface.) Find a new one for 80 bucks shipped from eBay Germany (not trying to buy a new set that don't have solid pictures of the surfaces). Put everything back and see if I might need to buy. STILL rough.

Today 20220625 new injector comes and swap it out. Check for vacuum leaks, check all connections.... STILL ROUGH. Still my favorite car I have ever owned. Just don't think I can get this going stock, I just wish I knew what this was. I have been holding off putting on my APEXi Power intake, buy some 550cc injectors, and want to get my ct26 rebuilt with 57mm impeller but I cant justify any of it with a rough idle. I am very frustrated. On the bright side, I can swap out injectors within 2 hours with all of the EGR crap in the way. Anyone thinks I missed something please bring it to my attention. I don't want to fuck my car up by modding before its ready.

 

[trofimovich]

Look at the ignition system. The fuel injectors are powered by 3 lines. They either work or they don't. But the ignition system can give a floating defect. That is, a spark on a candle, or not. The ignition system also has 3 control lines. This line from the control computer to the spark plugs contains a crankshaft position sensor, a switch, power wires, etc. The car is old and therefore the wires are often dry. The insulation cracks and water spoils the copper. If improvements appear after the repair of the crankshaft position sensor, then you need to move further in this direction.
Try rewinding the engine harness wires. Power is supplied to the coils with a weak wire. Contact is often lost signal in the connector. And in the place where the wires pass above the cylinder head, the wire to the crankshaft position sensor often breaks. New wires and connectors will help avoid a floating defect.
When the wiring harness is excluded from the fault chain, then it will be possible to change sensors .
UPD if the shielded wire from the crankshaft position sensor is damaged, the computer will give an error and may have a signal defect. The computer will give a signal to the igniter that is not correct. There will be a pass to the coil. It is necessary to exclude the engine wires from the list of defects and then look for a malfunction.