wrccruz

Can anyone please give me some advice? My 86 300ZX runs perfectly smooth until it warms up. Then on acceration, I get a really bad flucuating idle and the car will hardly run at all. Once again, on idle it is fine. Just on acceration. I have done all the usual maintenance things as well as the fuel filter and pump. All vacuum lines have been replaced and the MAF cleaned. Any recommendations would be greatly appreciated.

zxguy1986

Could be one of a number of things. First I would check throttle position sensor (TPS) or 'throttle valve switch.' A new one may not be available OEM but aftermarket is OK there. Check and clean the connectors on it first. (See page EF & EC-3 - and following -in your factory service manual (FSM) - which you DL as a freebie from XenonZ31 Reference . Lots of diagnostic and troubleshooting pages which are easy to follow. Other cool docs there too.

If that doesn't do it, report back with the symptoms again so maybe we all can get what is going on. Are you saying that you start the car, you warm it up at idle. Then when you accelerate, the engine hesitates as the rpms increase - or it does not accelerate at all? OR, are you saying when the engine is still cold, it drives and accelerates fine through the rpms - but when it is finally warmed up, the acceleration problem shows up? We need to figure out if it is purely temperature-related or purely mechanical/electrical regardless of temperature. Thanks.

wrccruz

I have cleaned all the circuits and plug-in on all the electrical connections. The car runs near perfect when cold but after warm-up when I try to accelerate, while holding the throttle half down (around 2000 rpms) it will loose power as if it is not getting gas. It will flucuate down to a normal idle back and forth making it undrivable. My guess is the IACV but totally lost. Thank you for your help. Def temp related.

zxguy1986

OK, sounds like a temp sensor (or the TPS) is sending wrong or no information to your ECU. I guess you replaced the CHTS (cylinder head temp sensor) because they're cheap enough - if a little hard to get to. IACV on a your Z is probably the idle-up solenoid on your air regulator - but that is probably working OK or the car would not hold idle at all.

Also, you ran an ECU diagnostic and got any codes it is putting out? If not, give it a shot. ECU can sometimes point to the problem area. It definitely knows things aren't right at this point. (Diag begins on EF&EC-35 in your FSM) Had a similar prob with my '86na a few years back but have to look up what we did. Will get back to you here. Thanks for the clarification.

wrccruz

I really do appreciate your suggestions. I will change that sensor out this afternoon after work. I even found a youtube vid where the dude shows a short-cut on how to change out the sensor. Yes, it does look like a pain to get to but way better than having a disabled car...lol. Will let you know how it turns out. Thanks again- Wil......The Cruzmyster

zxguy1986

If you go aftermarket (NAPA, etc.) for a replacement CHTS, they call it 'coolant temperature sensor' or something like that. Best to just bring the old one with you and hand it to the parts computer jockey. He will order something or other. Next day, bring the original back there when you pick up the supposedly correct part. Check to see if it will actually fit before you leave with it... Can save you some time...

Zuphoria

After the car is warmed up, unplug the MAF and start the car again to see if the problem goes away. If it does, your MAF is done.

wrccruz

Ok....I changed out the CHTS and checked the MAF as suggested with no change at all. The CHTS was really hard to get to as the video shows on youtube and it did need changed it looked really burnt and was glad to have the new part but disappointed that it didn't solve the issue. Any new suggestions would be greatly appreciated. Thank you....Cruzmyster

zxguy1986

I suggested above that you run a diagnostic through your ECU. (Called ECCS in your manual, diagnostic starts EF&EC page 35) In spite of the electronic complexity of your Z, you have an early model ECU ('86!) and it cannot tell you EXACTLY which part to replace like the newest ECUs do - but it does know if there is a major problem somewhere and usually tells you the area to check - if not the exact part. That info can be valuable.

I know it would be cool if someone here already had the exact problem you have and could tell you the instant solution - but nobody here has driven your Z or heard and felt what you do when you drive it. It's hard to describe a mechanical/electrical problem in a way that everyone understands or can recall happening the same way.

If you can come back with whatever codes your ECU is putting out, it could help here. If it's putting out no codes, that's good information too. Why not give it a shot? Otherwise you can only get a big shopping list of things to check/test/replace from the guys here... and that's probably not what you want at this point. It's your call. Thanks!

wrccruz

Yes Sir, you did suggest getting the codes and I plan to do that tomorrow afternoon. Before working on it today, I did have the battery disconnected for a bit so it may be cleared out. I will let it run for a bit tomorrow and check to see if there are any codes after it warms up. Today for the first time, the idle flucuation problem happened while the engine was cold. Don't get me wrong, I am always happy to replace parts on my car but disappointed in myself for not being able to figure this silly issue out. I feel like it is something simple that I may be over-looking and frankly, its getting on my last nerve! LOL....I appreciate any and all suggestions and will be looking forward to hearing input.

joselitopr

I do have the exact same problem.And I still trying to find out the problem for the last 2 month. I just remove the inlet plenum removing injectors today and replacing distributor and Fuel injectors connectors and the MAF.I let you know the outcome

wrccruz

ZXguy1986....you were dead on the money. The coolant temp sensor did the trick after all. I had to replace the connector and as soon as it was replaced, my Z car is running perfect again. I also replaced the connector on the IACV. I ordered the connectors off ebay and had to wait for them but saved a ton of bucks. Autozone had the connectors but wanted 32 bucks for each when I found then for 12 on ebay. Thanks for the great advice. You should do this for a living! LMFAO.....

zxguy1986

Good job! and thanks. That stuff is why we are here. (By the way, this could mean your old CHTS was just fine. It was the harness connector... )

Now you have me wondering what your ECU was putting out during all that time... We'll never know. Any chance you can run the diagnostic now that your Z's running right? The codes, if any, could be a help to others here. There's a chance you get an all clear signal - which would be vewy kewl

wrccruz

Being a slave to the dollar time is really going to be short for me over the next few days but I do plan to try and check for any residual codes. My next big project is going to be cleaning out the throttle body, plentum and replacing the injectors/hoses and all connectors involved. Thinking about new valve covers while I have it all tore down as well.....anyways, here the vid that helped me through this project. Thanks again for your help!

wrccruz

Oh yes, my CHTS was all melted and sidewise so it was truely needed....LOL