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Discussion Starter · #1 ·
Hey guys my 93 P10 is having a rough idle i thought it was the cap and rotor but, when i changed it nothing happend. so i looked on the web and found someone who told me to check the spark plugs and wires. so while the car was running it pulled the spark plug wires to see if idle would change. cylinder 1 no change in idle but cylinder 2-4 the idle would change. i don't know what that means as i'm still new to modding the car but if you have any idea what it could be please hit me up and if you need to know what is done to the car so far i can tell you if it will help diagnose the problem

thanks guys
 

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Put in a replacement spark plug (NGK brand BKR6EGP) in cylinder 1 and start the car. (If you have a rough idle still, it probably means the fuel injector on cylinder 1 is bad. (I'm assuming the car runs with less power when you drive it. Not good to do-driving with a bad injector.) The fact that the idle changes when you remove the plug wire from cylinders 2 - 4 just means that they are functioning properly until YOU disconnect them from their source of spark. That the idle doesn't change when you disconnect the wire from cylinder 1, shows that cylinder 1 has something wrong happening with it.
If you pulled off the plug wire while the engine was running, it is to be expected that that cylinder would not be getting spark, and produce a rough idle. (You disconnected the SPARK plug wire from the plug, so of course the plug will not fire.)

Before you buy a new set of plug wires, I would test the fuel injector on that cylinder.
To test an injector, you have to disconnect the plug on the back of that injector. Press the plastic release button on the under side of the injector at its base and remove the plug from the injector.

To test the injector, use a digital multimeter, a cheap one will work fine ($15 at an auto parts store or even Wal-Mart).
Make sure it has a battery in it.
Turn the dial to the Resistance setting (Ohms) closest to 20 Ohms and test by touching the two test leads to the two little prongs inside the injector's plug housing. You have to feel for the two little prongs with the test leads, and be sure you are not touching the same prong with both test leads. The range of "good" is 10-14 Ohms. Over 14Ohms means there is too much resistance in that inkector and you can expect poor performance from that injector/cylinder.
 

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Discussion Starter · #3 ·
thank you ill try that ill check the injectors first before i buy the spark plug wires and your right it did have little to no power when i drove it. i would have to keep my foot on the gas to keep it from idling too low also while driving i think its a fuse issue but my turn signals stopped working as well
 

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Ok. Post what you find after testing. If by chance the injectors test "good", you can test the resistance from one end of that spark plug wire to the other. Remove it from the engine completely. Put one test lead on one end of the metal inside the boot and the other inside the end the spark plug enters. Do a search on here for the "Spark Plug Wire Resistance", or refer a FSM factory service manual for those specific Resistance measurements. The shorter the plug wire, wire the lower the resistance, logically. But if the multimeter reads [ 1. ] or some high number or continues to climb, the resistance of the wire is too high, and the wire is bad. In that case, you would need to replace at least that wire, but better off just replacing the set, given that is how they are sold.
 

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Discussion Starter · #5 ·
hey sorry for the long wait to respond but yes only the one fuel injector was bad i replaced it along with some other maintenance for the car and its running way better now thanks for the help
 
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