redtop sr not reving properly after idling

[240_sxcoupes13]

I just started having this really weird issue with my redtop sr.

The car starts and idles quite well. Upon start up it will rev up like it should for a while. Then after a few minutes it starts to have some issues, when giving it about 1/2 throttle and holding it their, it will only rev to 2000 rpm then sputter and drop to around 1500 and repeat. If I shut the car off then restart it immediately it idles fine and can rev freely for a bit, but again after a few minutes it begins the same routine.

I checked the plug on the maf its seems fine, when I unplugged it the car started to die, then went back to normal after i plugged it back in. Voltage on the cas showed 0.48 which I believe is normal? Also checked for boost and vacuum leaks.

mods on the car are as follows:

550cc injectors
z32 maf
s15 t28
fmic
sard FPR
Aeromotive 340 lph fuel pump
HKS intake
Nistune ecu with RS enthalpy rom tune.(I don't think its the tune it ran great for many months, I used to commute 110 miles with the car everyday)
Everything else is oem

I do have a Nistune software license and consult so I could hook it up and see some of the engine parameters, but I have zero experience with tuning so I wouldn't really know what to look for. Any ideas to help diagnose this problem would be greatly appreciated.

[TomBec]

checked the tps?

[Kingtal0n]

I would try a new maf first.

Then, the cheapest/easiest route for diagnosing this issue next, is to replace the entire setup back to OEM (injectors/maf/ecu)

Its really simple if you have the OEM fuel rail with OEM injectors, only 3 bolts and its changed over. I always keep the OEM rail+injectors handy for that.
Same with the ECU, 1 bolt,
and the maf, 1 hose clamp


otherwise, your troubleshooting is more difficult. You can check the fuel pressure. Check for boost leaks as well.

It sounds like a boost leak to some extent. When you first start the engine the turbo is cold(er) so there is not as much net movement of air molecules in the plumbing, so a leak (small tear in a coupler) will not become apparent until the exhaust really starts to heat up and the turbo gets spinning... then that small tear becomes a problem.

[ultimateirving]

Op something like this happening out of the blue could point to a vacuum leak and is a easy fix(if you are so lucky). It would be best to build a boost leak tester and pressurize the intake plumbing.

If you have never done a boost leak test it is something every turbo owner should do semi frequently. Sadly things dry up and wear out and the heat cycles do cause a bit of wear and tear.

[240_sxcoupes13]

It sounds like a boost leak to some extent. When you first start the engine the turbo is cold(er) so there is not as much net movement of air molecules in the plumbing, so a leak (small tear in a coupler) will not become apparent until the exhaust really starts to heat up and the turbo gets spinning... then that small tear becomes a problem.

Thanks for the input guys,

I already did a boost leak test, also all the vacuum lines have been replaced within the last year so i doubt any of them would have ruptured i checked and they are all still connected in there proper locations and can't hear any leaks.

Like I said even when the car is brought up to temperature, If i shut it off and restart it immediately it Idles and revs perfectly, then starts having issues after a few minutes. I had the car idling for over 2.5 hours straight on the weekend, and restarted it 15+ times trying to get to the bottom of this, it did the exact same thing every time. Idles perfect at ALL times, but only revs up for the first few minutes after start up.

I'll check the TPS and I think i still have most of the oem parts so ill probably change everything back over the weekend and see where that leads me.

Thanks again everyone.

[ultimateirving]

Since you mentioned "when the car is brought up to temp." The cts could also be a culprit, it tells the Ecu when the car is up to temp and could cause some idling issues.

[240_sxcoupes13]

Since you mentioned "when the car is brought up to temp." The cts could also be a culprit, it tells the Ecu when the car is up to temp and could cause some idling issues.

By saying brought up to temp I just meant the engine is warm and has been running for a while, meaning it starts and revs perfectly fine even when the engine is warm but only for a few minutes. The car has ZERO idling issues. Idle is perfect and steady all the time even when its having the rev problem.

I'll still look into it though, how do you test the coolant temp sensor?

[ultimateirving]

By saying brought up to temp I just meant the engine is warm and has been running for a while, meaning it starts and revs perfectly fine even when the engine is warm but only for a few minutes. The car has ZERO idling issues. Idle is perfect and steady all the time even when its having the rev problem.

I'll still look into it though, how do you test the coolant temp sensor?

Quick google search turned this up

http://240-sx.net/testing-coolant-sensor/

Seems like decent instructions on what to test