# rough idle at high temp, horrible gas mileage



## tvnner (Jul 9, 2021)

i have a 1991 nissan hb ka24e, when i first bought it it was running like a dream. After the first month or two the idle started to surge. i thought it was the maf so i replaced it and only made things worse. i went ahead and cleaned my injectors, new spark plugs, new o2, new vacuum lines, fuel filter, oil change, changed fuel pump and it still struggles to idle correctly and now i have terrible gas mileage. It’s running very rich so idk what it could be. The other day on the freeway i was driving and noticed when i went to a stop the motor was ticking. when i got home it went away, could my oil pump be going out and causing it to pump improper amounts of oil? The timing chain sounds like it’s slapping between 2500-3k rpms. I checked the guides and the previous owner changed the guides and tensioner. i haven’t checked my oil pressure but im sure it’s low. Any ideas of what this could be, been having a hard time figuring out what it could be and been dealing with it for a couple months.


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## jp2code (Jun 2, 2011)

Probably a bad injector. Running the fuel injector cleaner flushed out the sludge in the injector that is stuck open. Now it leaks all the time. 

That's just an educated guess. 

On the MAF, if you unplug it and the engine idles fine, the new MAF is bad. MAF sensors rarely go out. Usually they need cleaning with MAF cleaner from the auto parts store. New MAF sensors often don't work well because they are built cheap and everybody buys them. Try cleaning the old one.

But, to make sure that you are not replacing parts for no reason, you should read the codes from the ECU. 






[VIDEO] Checking Error Codes - Infamous Nissan - Hardbody / Frontier Forums


[VIDEO] Checking Error Codes Hardbody Forum (D21)



www.infamousnissan.com


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## BRubble (Jun 22, 2014)

tvnner said:


> i have a 1991 nissan hb ka24e, when i first bought it it was running like a dream. After the first month or two the idle started to surge. i thought it was the maf so i replaced it and only made things worse. i went ahead and cleaned my injectors, new spark plugs, new o2, new vacuum lines, fuel filter, oil change, changed fuel pump and it still struggles to idle correctly and now i have terrible gas mileage. It’s running very rich so idk what it could be. The other day on the freeway i was driving and noticed when i went to a stop the motor was ticking. when i got home it went away, could my oil pump be going out and causing it to pump improper amounts of oil? The timing chain sounds like it’s slapping between 2500-3k rpms. I checked the guides and the previous owner changed the guides and tensioner. i haven’t checked my oil pressure but im sure it’s low. Any ideas of what this could be, been having a hard time figuring out what it could be and been dealing with it for a couple months.


TV,

JP said:
"But, to make sure that you are not replacing parts for no reason, you should read the codes from the ECU."
^
^

How many mile's on your '91?

Think back before the problem began ie, were you doing Rough Roading, Excessive Spinning, etc? How's the Cat or Cat's, I don't remember how many cat's I had on my '93 with Ka24e engine.

Is it possible that you have or had some Water Consendation in the Gas Tank? Might be worth putting some Techron in the tank @ the Gas Station and then fill up the tank to mix good. Every few year's I had to do that with the '93 that I had.

If the Timeing chain make's a rattle @ startup but then go's away, that's normal, but if you continue to hear it,, then that need's to be addressed asap IMO.

Stop Throwing Part's @ the Wall hopeing something will stick. Too Expensive and Depressing to continue doing that. Sometime's we have to do that though, after the Strategic Plan has been gone through.

Good Luck,


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## tvnner (Jul 9, 2021)

How


BRubble said:


> TV,
> 
> JP said:
> "But, to make sure that you are not replacing parts for no reason, you should read the codes from the ECU."
> ...


i have 133k on the stock motor, i checked my ecu codes multiple times and the only code it throws is a temp sensor which i have u plugged because im using an aftermarket intake. Also throws a ecm code but it’s ever so often, u think it could be my ecu?


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## jp2code (Jun 2, 2011)

tvnner said:


> How
> 
> 
> i have 133k on the stock motor, i checked my ecu codes multiple times and the only code it throws is a temp sensor which i have u plugged because im using an aftermarket intake. Also throws a ecm code but it’s ever so often, u think it could be my ecu?


The ECU uses the temperature sensor to calculate the air/fuel mixture. If it cannot see the signal, then the ECU will run the engine in limp mode.


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## VStar650CL (Nov 12, 2020)

jp2code said:


> The ECU uses the temperature sensor to calculate the air/fuel mixture. If it cannot see the signal, then the ECU will run the engine in limp mode.


+1. Bad IAT's (Intake Air Temp) are a prime source of bad gas mileage complaints anyway. Most Nissan IAT's go to -22F or -44F when disconnected, so the ECM thinks it's in Alaska and drives the mixture way rich.


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## BRubble (Jun 22, 2014)

tvnner said:


> How
> 
> 
> i have 133k on the stock motor, i checked my ecu codes multiple times and the only code it throws is a temp sensor which i have u plugged because im using an aftermarket intake. Also throws a ecm code but it’s ever so often, u think it could be my ecu?


TV,

Sound's like JP and VStar has a good path to follow IMO. They know more than I ever will know anyway, except VStar should be rideing a Harley. 

I hope that the Running Rich Condition hasn't clogged the Cat or Cat's, and if what they recommend get's you on the right path, then it probly wouldn't be a bad idea to pull the plug's and see if they are badly caked with carbon. If so replace with OE is my advice. I can't remember if mine were NGK or Nipon Denso. Best to stay OE, IMO so don't have to think about correct heat range.

Stay away from Mod's to the Engine, as it lower's resale value IMO. Be extra careful with Battery connection's and if they are corroded, clean up with bakeing soda, tighten clamp's and Coat heavy all bear metal with Multipurpose Grease. I know doesn't relate to this problem, but crossed my mind when reading about ECM and Electrical Spike's. The ECM doesn't like'm. 

Hope thing's start looking up now.


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