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How to Diagnose Nissan Skyline Idle Problems

Dreaded Fist writes about Nissans and about modifying cars for high performance.

The Nissan Skyline is legendary, thanks to far too many appearances in video games, movies, and manga. While the car is certainly way too much fun to be legal, it's not without its problems. The RB series of engines that powered the most desirable Skylines (we'll say the cutoff point is the RB20DE, anything lower is probably not worth fixing) have a habit of developing idle problems, particularly as they work their way into their upper teenage years.

As the owner of an RB20DET-powered R32 GTS-t, this author has experienced and dealt with the aforementioned RB idle problems. What was supposed to be an easy diagnostic and fix turned into an expensive ordeal. But hey, that's Skyline ownership for you.

Instead of covering the R32, R33 and R34, I'll cover everything that could possibly cause an idle problem across all three generations of the car. I suppose this guide could also cover the RB20-powered R31 Skylines as well, though I'm not 100% sure about that, as I believe there are only one or two R31 Skylines in all of Canada, and I've never actually seen one in person.

Is it REALLY that hard to hold a steady idle, you stupid engine!? * Throws wrench across the front yard*

Is it REALLY that hard to hold a steady idle, you stupid engine!? * Throws wrench across the front yard*

Pops, Misses, and Stalls

There's a good chance that if you ever find yourself owning and driving an RB-powered Skyline, you'll also run into the inevitable idle problems. These typically manifest themselves as pops, misses, or stalls caused by rpms dropping. In this author's case, it started as a slight pop now and then, turned into a very audible "miss," and then manifested itself as stalling when coming to a stop and stepping on the clutch.

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Diagnostics and Potential Fixes

When sitting at idle, the car makes a "pop" noise

A popping noise will typically also show itself as a very slight dip in rpm. The tachometer may show the rpm drop to be somewhere in the vicinity of 50-60 rpm. This typically happens after the car has warmed up to operating temperature.

  • Have you inspected your spark plugs lately? Pull them out and take a look. If the gap is too large, the plug may not be able to create a spark or may create a weak spark. If your car is older and the coil packs are original, you can decrease the spark plug gap down to 0.8 mm to help cover a weak or dying coil pack. If you're running higher than stock boost levels, you should gap to 0.8 mm anyway. If you have not changed the plugs since buying the car, change them now. New plugs can wake an engine up and make it feel like a brand new engine.
  • How do your coil packs look? You can use a multimeter, but most agree that if your car is 10+ years old and has covered more than 100,000 km on the original coil packs, you should look into replacing them. Coil packs can develop a hairline crack, which can cause them to ground out. Replace them with OEM coils (the best, but most expensive option), or aftermarket coils, such as those available from Splitfire or other reputable companies. When you replace your coil packs, you should also replace the coil pack loom, as they harden over the years and become brittle.
  • Check your throttle position sensor (TPS). You can test the sensor with a multimeter. Tie into the middle wire in the group of three wires that are at the bottom of the connector (this is on the R32 GTS-t, it may be different on the R33 And R34). The TPS should give you a reading of .48. Honestly, if the TPS looks old, you should replace it as routine maintenance, as they only cost about $40.00. Make sure it's adjusted to .48 after you install it.

When coming to a stop, the rpms drop, causing the car to stall

Nothing is quite as annoying as having to give the car some go pedal every time you come to a stop, to prevent the engine from stalling.

  • The throttle position sensor (TPS) is responsible for helping your engine maintain a proper idle. There is an idle contact within the TPS that is supposed to touch, making the car go into idle mode. If the contact isn't touching, it is possible that the revs will continue to fall as the engine doesn't "know" that it's supposed to start idling now. A quick way to test the TPS is to give the plug a wiggle. See if the engine RPMs change. If continued wiggling of the plug causes the engine to stall, replace the TPS.
  • Do you have an aftermarket vent-to-atmosphere blow-off valve? Skylines are equipped with a MAF (mass airflow sensor), which means the air that gets vented by the blowoff valve has already been metered. When you vent that metered air, it causes the engine to run extremely rich, which causes impressive flames out of the exhaust, and unfortunately, stalling problems. If your car has the stock ECU and an aftermarket blow-off valve, you either need to re-circulate the blow-off valve back into the intake, after the MAF, or you need to get a re-tune of the ECU. A very dodgy fix is increasing the idle speed.
  • Clean your MAF. Don't use brake clean, whatever you do. There are MAF cleaners available that you can buy at pretty much any auto parts store. If you have been using an aftermarket air filter with an oiled filter element, throw it away and kick yourself in the shin. MAF-equipped cars hate oiled air filters because the oil eventually begins to mess up the little wire in the MAF. Replace the oiled filter with a dry-style filter, and clean your MAF.

These are the fairly common causes for Skyline RB engine idle issues. I'm sure there are plenty of other causes, but I've yet to encounter them in my travels. If you've had any problems with yours, let me know in the comments, and I'll add them to this article. Keep in mind that if you're rolling around in an R32, well, these are old cars now, and old cars tend to be maintenance queens. When you pick up an old sports car, it's pretty important that you replace just about everything you possibly can with your budget.

Don't even think about aftermarket mods until after you've replaced any old and tired sensors, cleaned the MAF, replaced the coils/loom/spark plugs, and inspected every other major component. Replacing the old vacuum lines is also a great idea, as you can be sure that there is probably a vacuum leak somewhere. Replace the fuel filter, fuel pump and injector loom as well if you can afford it. If you can't afford it, save up money until you can!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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