84NA mysterious problem

[Pitts]

After reading forums alll night last night (till about 5am) and doing some testing here is what I've come up with.

Diagnostic check: Codes 31 and 23 (AC isn't installed, so that explains code 31)

TPS: I can either get millivolts or battery voltage based off of adjustment. When it's adjusted to millivolts for idle, it does read at battery voltage when the throttle body is opened up. One of the wires reads millivolts for conductivity to the throttle body whereas the other says 9.4 volts. Which the FSM says to replace the TPS/TVS. Also read that I can unplug the TPS and if she runs better and I can apply throttle, it's a good sign that the TPS is out. I tried that with no change.

CAS: Tested the connector for the harness as the FSM depicts, I had good voltage from pin 1 (positive) but bad resistance from pin 4 (ground). The FSM says to replace the harness. While the ECU didn't give me this code, I still tested to rule it out.

Fuel Pressure: I've been eying the pressure every time I'm under the hood. It's had between 30-36 psi (depending on load when it ran yesterday).

Coil, plugs, cap, and rotor: Visual inspection, as well as tested and all were great.

Vacuum lines: I've recently replaced all the lines that are used (EGR, FPR, cruise control) so I know they are good.

Ignition timing: at 15 degrees.

Timing: belt and all gears line up perfectly.

For the past couple months she liked to act up when cruising (typical TPS/TVS issue). However, 2 days ago, she started idling rough and seemed to lack a little power. Then that night as I went out to pick up some pizza, I only made it about a mile downhill before she quit on me. Didn't have much to do a diagnosis there, so I did a couple small things such as pop the line off the fuel filter (which was replaced 3-4 months ago) and I barely had any fuel in the line. Which made me think of my fuel pump. Did the standard (for me anyways) sit and wait, then drive as far as possible (being careful to not stress the pump too much). So, the following day after I adjusted the TPS some, it ran great for about an hour and a half. Since then. I cannot get her to stay idling for long and if I so much as open the throttle body a millimeter, she stalls instantly. Tried running with the TPS/TVS disconnected and no change. It could be the fuel, I'll be running over to the gas station (it's not a long trip, maybe 120 feet to the pumps from my house) and trying some new fuel. While I highly doubt it will solve anything, sh*ts and giggles right? Grab a snack while I'm at it.

When I could drive it the other day and it started to act up, it would bog down horribly. For example, I'd be in second gear at 3200 rpm and it would basically act like I took my foot off the throttle and was using the gear to slow me down. Yesterday I could get her to idle while being towed home so I could apply the brakes. Today, I'm lucky if she idles for 10 seconds.

Anything else I should test?? I need my car as I do work tonight in 12 hours. Thanks.

[Pitts]

Got her to idle this morning (before adding more gas) and I took a video of her. In the video, you can see that I could barely move the throttle body without stalling her. Also did the TPS pin conductivity test and recorded it for you. https://www.youtube.com/watch?v=09gR9hv ... e=youtu.be

[Pitts]

Got her running this afternoon. From what I've seen yesterday and today, she seems to prefer starting up in warmer temperatures. Sat and varied idle for about 30 minutes and took a 5 minute cruise to go up a hill with a 67% grade slope. Didn't miss once. I also checked the CHTS after she warmed up and the resistance was less than 10 ohms. Going to have to check it tonight before I go to work (as well as see if she will fire up). While under the hood, I adjusted timing to 18 degrees and she's idling much smoother. Plus I tapped on the ICM a few times (with a flashlight) and no change, so it's highly unlikely that my ICM is the culprit. I'll keep updating as I try more things out.

[Pitts]

Got her to act up. Fuel pressure dropped to 30 psi and idle is erratic as well as high. Video: https://www.youtube.com/watch?v=hOhBAAd ... e=youtu.be

[Pitts]

It seems I have figured out the TPS and it's reading properly now. Although in the video with the continuity test, it still makes me wonder. But I was doing some thinking earlier based off what I've noticed when she was warming up and I opened the throttle. I'm thinking it might be my cat. Going to get her to act up tomorrow, take off the down pipe from the header, and hope she runs better. If she does, I'll let her sit overnight and then cut into the cat for a temporary fix (Montana has no emissions, I know I'm a lucky b**yard).

[Pitts]

Major Update:

Well, the cat wasn't an issue (while tons of water, it seems as it didn't smell like fuel, came out; but it also got to 35 degrees last night). However, I decided to clean all the connections I could. Didn't help any. Then I decided to test her with the MAF plugged in and unplugged. Major difference. When she was unplugged, I could idle and use some throttle. When she was plugged in, she died instantly under any throttle change and the idle was erratic. So, I'm going to my local pick and pull to grab a MAF (they have 2 parts cars, will try to grab both if available) as they only want $10-15 each. I'm sure if I walk in with a $20, I'll get them both (if available). Might bring an extra $20 to grab the TPS's as well.

[Pitts]

Good news and bad news. Good news, TPS is good as I bought 2 spare ones and tested a new one off the shelf (it pays to know everyone at the parts store sometimes). Bad news, cleaned the MAF, no change. One of the parts cars didn't have a MAF and the other one, well, the entire intake had oil in it (was rolled) and no sense picking a MAF that was contaminated by a lot of oil (enough so that oil dripped out of the intake and didn't look that old (been in the yard less than 3 months). Trying to source one from other yards in the state.

[evildky]

You said you had high resistance int he ground wire from the cas? you might want to check your battery to chassis and engine to chassis grounds, as well as the grounds from the harness itself and possible backtracking into the harness where the multiple grounds come together, it's generally a crimped connection covered in goo but can breakdown over time.

[Pitts]

Thanks for the tip. I think I might know the main culprit for the ground issue. I've noticed that the negative cable (where it is held to the chassis; next to the battery) has some build up. I'll do a resistance check before and after that spot to see how much of an issue it is. Found a MAF about an hour from me. Going tomorrow to get it. Wish me luck.

[Pitts]

Well, the tip on the MAF was a bust. Guess I will grab the one from the local yard here that got oil on it. Clean it up well and hope for the best.

[Pitts]

Good news and great news. That MAF (contaminated with oil) works perfectly after some gentle, but rigorous cleaning with CRC MAF cleaner. My O2 readings are exactly where they should be now. Now for the good news, due to the vehicle running better, my alternator is charging better (smoother). Plus, the MAF was from an 88 and the plug that the prior years had isn't there (for MAF adjustment) (correct me if I'm wrong on the plug not being on the later MAF sensors). Cleaned the chassis ground next to the battery and my resistance is .2 ohms compared to 1.98 ohms. Thanks for the tip.

Hopefully this thread helps someone out in the future if they took the same diagnostic steps as I did and got the same end results. Drove around for a couple hours to verify that the MAF wouldn't act up. So now, back to driving around with a boner. (Cat delete and muffler install next paycheck (has a glasspack in place of the muffler currently)). Thanks again Evildky, enjoy the sun.