91 NA Hard to start and stumbles when cold

[solaire]

So this is the same car I had from another thread up here. I finally got it running after swapping the Cam sensor and detonation sensor

Now that that's out of the way, it's got new injectors, new plugs, a good CAS, PTU and ECM. I had it running beutifully yesterday exept one thing. It wouldn't idle under 1200rpm. Also atm I have no battery and was using the truck to jump start it with jumper cables (and truck running) idk if that's my issue or not?

Guy stopped by and wanted to hear it run before he brought the battery (tomorrow he'll bring it) I told him It was running great yesterday so I proudly started it today and it ran like total crap, stayed running but wouldn't idle up past 1000rpm and just ran rough. I know they're supposed to raise to 2000rpm when cold so that's probably why it ran bad. I was scratching my head checking for loose connectors and after a few mins it cleared up on it's own and the owner was all smiles then it bogged out and ran like crap again. I wiggled the coolant temp sensor and it cleared up. Idk if it's coincidence or related. The connector isn't corroded and the sensor looks fine but here's my theories:

Do I have an intake leak? When warm it won't idle under 1200rpm and if I adjust it down to 1000rpm it seems to start to run crappy.

Could it be that coolant temp sensor keeping the idle from dropping?

Could it be that not having a battery is causing eratic voltage in the system causing the problem? He said he's "Charging" the battery he's going to bring me so idk if it's going to be any good or not. Definatley won't be a new battery.

[ZL8NING]

You are really fighting gremlins with this car!

Maybe you can borrow the battery from the truck, if it will fit. But that -ve lead to the battery on the Z is very short! I had that problem the other day when I tried to borrow the battery from my Legend.

Good luck.

[solaire]

My truck has a side post. No dice. I'll see what happens tomorrow when I get a battery

[Ziggy1621]

Yes, the CTS can screw with the idle. Check the ECU for codes - 300zx-z32-ecu-diagnostic-t249406.html

[solaire]

I really dont feel like taking this guy's floor back apart but it looks like I may have to. If cts is the problem it acts like it wouldn't throw a code but read incorrect temps (still be in spec but not reading right temp for conditions). I could tell that by looking at ECU data but that usb consult plug i bought of ebay won't work for some reason. ECU talk and conzult can't see the plug in their COM ports.

[t.mcginley.jr]

A bad CTS will also make the ecu mess with the timing, causing all kinds of problems like you're describing. The not being able to idle below 1200 rpms sounds like a stuck IACV to me, mine would do the same thing when it was stuck even with the idle screw all the way adjusted

[solaire]

I checked CTS earlier today. Its got some corrosion on the sensor terminals but not the connector which seems to have been replaced before I got the car. Pins in the connector appear tight. I'm going to try with a wire brush and contact cleaner to clean the sensor up. I can manually adjust base idle but going under 1000 causes stumble so I raised it back up. But like you mentioned maybe the CTS is messing with the idle mixture and timing and the IAC is trying to correct it. I did remove and replace the IAC gasket while the intake was off as a preventative measure. The surfaces were very clean when I put the gasket on.
I should be keeping the car for the weekend with a new battery to make sure its done. Either way this gremlin filled nightmare will be going back to its owner unless it completely is undrivable. I don't mind this kind of work on my car but the owner knowing nothing about these cars has made this process more of a pain than it needs to be.

[ZL8NING]

Well, we all live and learn. I'm sure this ordeal has been an eye opener for him. You've also learnt a bunch from it I'm sure. Next time you see a thread where someone needs help with similar issues, you'll chime in with "try this....."

[solaire]

Yea I've learned a lot of tricks to use on my car too. Well it cranks and runs better when cold now but won't rev over 3000 rpm when in gear. Seems 1 & 3 are dead. Fuel fouled. Makes a nice thump and vibration when accelerating but its smooth revving in neutral. They both drop a nice blue spark so I'm lost. I may try swapping ptus again but i have a feeling its in the ptu connector thats corroded.Don't want to tell him its a compression problem. He won't believe that I didn't "hotrod" his car which I didn't and will probably try to sue me or something. I don't even drive my 90 very hard.

[Ziggy1621]

Hav you OHm tested the injectors on 1 & 3? You can also solder the wires for the ptu connector to bypass those plugs

[solaire]

The 1&3 injectors ohm checked bad and were pouring fuel so I replaced all 6 with a set from TFL performance on eBay. I pressure checked the rail before installing and had zero leaks at 55 psi. Could a stuck egr valve cause this? I know his feed line to the egr was disconnected when I got the car and I replaced all lines and reconnected it.

[solaire]

Today I checked wiring from ptu to the coils 1&3. I had good readings .2 ohms. I checked compression and #1 was 210 and #3 was 0. I think I've found my issues. I'm going to do a leakdown test tomorrow to see where #3 is going but the fact that #1 compression is higher than spec it could be leaking into #1 via the head gasket. I'm not 100% for sure because if that was the case #1 could leak into #3 but it doesn't. Has anyone seen this before? I'm also trying to figure out how this isn't going to be linked to me driving the car maybe 3 miles and idling in the driveway a few times with bad injectors.I'm not sure if it was something I did or not. I don't think so.