So a year ago I bought 79 280zx, I did everything to it from cleaning out the entire fuel system, cleaning the afm, valve adjustments, trying to clean the throttle body, I blew air through injectors and the fuel rail, sealed the tps after cleaning it, changed spark plugs and wires, ran fuel cleaner through it, and changed the plugged pcv tube, changed one injector to get rid of a misfire which it succeeded at doing, checked for vaccum leaks, corrected timing. It also would sometimes start up and the idle would go up and down and after driving for a bit it would stop the bad idle and it rarely stalled but started stalling more and more at only the first stop light times the idle was bad and also sometime later into owning it, it started randomly somtimes dropping rpms on the freeway, the idle didnt really matter on it being winter or summer, but the rpm dropping was when it got warmer. Oh and its straight piped and cold air intaked. Recently I got a 83 280zx after rear ending someone with the previous one and without doing much to it, it had way more power already the first time I drove it. Any one have any other ideas as to why it was this way? I've looked everywhere for a while as to why. If I can figure this out it would be a really big accomplishment.

 

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Did I hear a compression check anywhere? when you are having problems you need to diagnosis and work the issue, not throw parts at it and hope for the best, or take random suggestions made based on limited info. I sometimes will throw out a suggestion but its often wrong due to my having to take a SWAG at the issue due to limited info.

Therefore I would recommend:

Compression check, fuel pressure, timing just for starters.

Tune up consisting of fluids, filters (air oil gas). Oh and a check of valve lash, adj if needed, very easy to do on a Z.

Next up would be some new plugs, drive the car several miles then pull them and read for clues on mixture and oil blow by.

listen for a misfire if noted do a balance test to find the offending cylinder, work the problem from there, has to be compression/fuel/spark. Resolve and test again.

There is a process to diagnosis, the FSM covers most of the problems you are likely to encounter. Common problems are poor fuel delivery due to plugged lines, and poor electrical connections on the FI. Sensors on critical for correct fuel/air mix, a reading of the plugs is a good start for this.

forgot to mention, on the bypass as others have noted, if you have a problem with it, you need to correct. Test it to see if it is functioning as designed (added air flow during warm up) using the FSM as a guide. If its malfunctioning replace it. One other item would of course check the vacuum hoses since you mentioned a whistle noise. Vacuum leaks are bad. Make sure the distributer is advancing as designed (there I go with a SWAG).

 

 

 

Edited August 20, 20177 yr by Dave WM
could not help myself

He's selling the 79.  He was just looking for a simple answer to a complicated question.

 

11 minutes ago, Zed Head said:

He's selling the 79.  He was just looking for a simple answer to a complicated question.

 

Roger, wish I had paid more attention, would not have bothered I had realized he was not interested if fixing it. of course the easy answer is there is no easy answer

on second thought, if you are going to have old cars that don't have all the ODB stuff, then the simple answer would be a lot of things could cause the problem and you have to diagnosis it to determine them using proper test procedures and keeping track of results.

Edited August 20, 20177 yr by Dave WM

 

5 minutes ago, Dave WM said:

on second thought, if you are going to have old cars that don't have all the ODB stuff,

Are you a Wu Tang fan?  Where does ODB come in?  Old Dirty Bastard.

8 minutes ago, Zed Head said:

 

Are you a Wu Tang fan?  Where does ODB come in?  Old Dirty Bastard.

yikes! had to look that one up.

OBD

Edited August 20, 20177 yr by Dave WM

I just want someone who has had this issue, and it could be air fuel ratio, but a smog machine is needed for that I think

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Also timing is perfect

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9 hours ago, thetech101 said:

I just want someone who has had this issue, and it could be air fuel ratio, but a smog machine is needed for that I think

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or you could read the plugs, should give a decent idea of A/F mix. all a moot point it would seem. Your looking for an explanation without enough data to draw a conclusion from.

I could but, but I'm looking for someone who has had this, not guesses. It would be nice to figure this out due to there not bring a forum any where without this issue and I'm sure there will be someone else with issue. In addition I just want to sell that car. it would be cool if someone happened to have seen this idle and the issues it developed before.

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With the issue*

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