does anyone know out there????

98_frontier · Apr 15th, 2006, 08:56 PM

i have a 1998 frontier 2wd and for the longest time i have searched and read but cannot find out how to adjust my idle.i know theres a rubber cap in front of it with a small opening but i have no idea what kind of bolt is behind it.anyone have any pics of how to do it or what tool to use?

ihscout54 · Apr 16th, 2006, 02:29 PM

I'm not 100% sure off the top of my head about a 98' frontier, but ill try to help
you are not specifying why you want to adj. youre idle. Proper idle speed in neutral for the frontier ka24 is like is 800 +/- 50 rpms the computer sets it via the iacv
if youre significantly off from that then heres a few posible causes
vaccume leak
power steering switch
coolant switch
engine temps
oxygen sensor
iacv
timing....
if you still want to adjust the base idle speed with the screw you speak of it should be just a flathead screw
note: if you turn the screw too far out the throttle may stick, and too far in the ses or check engine light will probably illuminate
i could get a diagram that may help but how to post it?
-Sam

himilefrontier · Apr 16th, 2006, 03:21 PM

There are 5 ways the idle is controlled on a 1998 Frontier with a KA24DE. The first, is the ISC solenoid. There is a fuse in the dash for it , IIRC it's marked IAV-SOL or something similar. If it's not working, check there first. Second, is the cold-start "Thermal Unit" on the throttle body. It goes up and down with coolant temp and is a mechanical device ( kind of like a heated choke on a carb). It acts on a roller which in turn acts on a cam on the back of the throttle body. The roller should be between 2 marks on the cam when the engine is cold. This adjusts with a set screw that rides on the thermal unit. Then there is also a seperate Idle speed solenoid that energizes with the A/C compressor. Also, the ISC solenoid's "Vacuum leak" can be adjusted with a black plasticv screw that is set inside the front of the throttle body on the left hand side in a circular hole. Finally, there is a set screw on the throttle body that the FSM says "DO NOT TOUCH!!!!" For more specific instructions, Download the FSM at http://carfische.com/. They don't have a 98, but the instructions are the same for all 98-04 Frontiers with a KA24DE. It's a free DL , BTW. I just went through all of these systems on my 98 Frontier with 234,000 miles and was able to get it right. Feel free to IM me if you need any more help.

98_frontier · Apr 16th, 2006, 08:44 PM

the ISC Solenoid "vacuum leak" thats adjust with a black plastic screw.is that located on the right side of the TPS nearest tp the valve cover?

in my maunal its shows the area and part you telling me as the idle adjustment screw??????

i put in cams in my truck and thats why i need to adjust due to uneasy idling....

himilefrontier · Apr 17th, 2006, 05:58 AM

Well, the reason you are having a time of it at idle then is because of insufficient low RPM cylinder pressure. If they were cams for a 240SX, they were designed for a point or so higher compression ( it's one of the many differences between the 240 and truck KA's). The black screw in the tube is the one to adjust then. Try using a vacuum gauge while doing it and tune for highest manifold, not ported vacuum. Alternatively, you could see if anyone has adjustable cam gears and degree in the cams so that you have a wider Lobe Seperation Angle. This builds more low rpm cylinder pressure due to a shorter overlap period, but wide LSA's typically give up a little on the top end. ( remember that big cams do not cause poor idle quality in and of themselves, low cylinder pressures do! Raising the compression 2 points or so would probably make it idle like a stocker!) You also want to be sure you have the cam followers shimed to the right valve lash. Out of curiosity, what modifications have you done to the engine? What cams, header, exhaust, head porting etc?

98_frontier · Apr 17th, 2006, 06:37 AM

well im i just tried the cams, a turbo muffler and exhaust im gonna swap the engine out for a napz.

98_frontier · Apr 17th, 2006, 06:39 AM

Quote:

Originally Posted by himilefrontier

Well, the reason you are having a time of it at idle then is because of insufficient low RPM cylinder pressure. If they were cams for a 240SX, they were designed for a point or so higher compression ( it's one of the many differences between the 240 and truck KA's). The black screw in the tube is the one to adjust then. Try using a vacuum gauge while doing it and tune for highest manifold, not ported vacuum. Alternatively, you could see if anyone has adjustable cam gears and degree in the cams so that you have a wider Lobe Seperation Angle. This builds more low rpm cylinder pressure due to a shorter overlap period, but wide LSA's typically give up a little on the top end. ( remember that big cams do not cause poor idle quality in and of themselves, low cylinder pressures do! Raising the compression 2 points or so would probably make it idle like a stocker!) You also want to be sure you have the cam followers shimed to the right valve lash. Out of curiosity, what modifications have you done to the engine? What cams, header, exhaust, head porting etc?

so i need to either retard or advance my cams for better idling?

himilefrontier · Apr 17th, 2006, 06:52 PM

KA> NAPS-Z ( The KA24DE evolved from the KA24E which evolved from the NAPS-Z, which is an evolution of the L20B which is a larger version of the L16b which was partially designed as a rip off of Mercedes Benz OHC 4's of the 60's by Prince which Nissan took over in 1966 or 65, IIRC). Well, you want to reduce the overlap, so you would advance the exhaust, retard the intake. BTW, cams are the LAST thing I would change on that engine! If you don't have a header, etc already, that is the first thing you should have done. CAms are best used as a last resort on modern engines as they don't do much to a otherwise stock engine which the OEM cams are optimized for. I would also consider milling the head for more compression.Provided you don't go too far and loose timing chain tension, it may be the best way to go.