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hi guys,

my turbo nb has acquired a funny idle problem and i think it may be the tps. i originally thought it was a vaccum leak but ive tripple checked all the vacuum lines and inlet manifold. ive also swapped the MAF with a spare and nothing changed.

the problem is.. the idle will hold around 1300 rpms as long as the car is moving, even crawling pace. it only comes down to 1k when the car is completely stationary. if i rev it, it trys to hang on the idle (floating around 1300 rpm) then slowly comes down to 1000rpms. sometimes it will hang around 1500 rpm when slowing down from driving (this is with the clutch in or neutral). idle is a little rough, not bad but it was better before the problem started. no power loss or anything like that, just this idle problem. my mechanic said to leave it, but 1300rpm + a/c + 40'c = 1600+ rpm and is probably not the best situation for a turbo nb through the summer.

anyone had this problem before??? is there a way to check the tps with the mutlimetre ?? anyone clean their tps with success?

psi-mx5 wrote:hi guys,

my turbo nb has acquired a funny idle problem and i think it may be the tps. i originally thought it was a vaccum leak but ive tripple checked all the vacuum lines and inlet manifold. ive also swapped the MAF with a spare and nothing changed.

the problem is.. the idle will hold around 1300 rpms as long as the car is moving, even crawling pace. it only comes down to 1k when the car is completely stationary. if i rev it, it trys to hang on the idle (floating around 1300 rpm) then slowly comes down to 1000rpms. sometimes it will hang around 1500 rpm when slowing down from driving (this is with the clutch in or neutral). idle is a little rough, not bad but it was better before the problem started. no power loss or anything like that, just this idle problem. my mechanic said to leave it, but 1300rpm + a/c + 40'c = 1600+ rpm and is probably not the best situation for a turbo nb through the summer.

anyone had this problem before??? is there a way to check the tps with the mutlimetre ?? anyone clean their tps with success?

If it is a NB variable TPS (and not an early NA TPS) then you should have 4 connectors. Unplug the connector and check that you have the following.

1) Between RED and BLK/BLU is a switch and should be on/off depending when the throttle is open/closed.

2) Between LG GRN/WHT and RED/BLK is a variable resistance that goes up/down based on throttle position.

3) Between LG GRN/WHT and RED is fixed resistance that should be the same amount as fully closed/open and never change.

Good luck.

G

What year model ???
What ECU are you using ???

Will Need to Know these thing before ANYONE can help

Russellb wrote:What year model ???
What ECU are you using ???

Will Need to Know these thing before ANYONE can help

its a 2001 NB, standard ecu with smt6 piggyback from AVO.

what i dont understand is why the revs stay high only whilst the car is moving... the only sensors that know the car is actually moving is the speedo drive and the abs. am i wrong??

went over the vacuum lines with a fine tooth comb and nothing, even replaced most of them just for the hell of it.

psi-mx5 wrote:

Russellb wrote:What year model ???
What ECU are you using ???

Will Need to Know these thing before ANYONE can help

its a 2001 NB, standard ecu with smt6 piggyback from AVO.

what i dont understand is why the revs stay high only whilst the car is moving... the only sensors that know the car is actually moving is the speedo drive and the abs. am i wrong??

went over the vacuum lines with a fine tooth comb and nothing, even replaced most of them just for the hell of it.

Engine computer knows when your are not in gear via neutral switch. So it doesn't know you are moving, but it does know the car is in gear and clutch is out (and so should be moving).

G

Have you tested the manifold for air leaks with car by cleaner. Have you tested the things connected to those hoses with car by cleaner? If you disconnect the IAC valve while the car is idling properly this will help you eliminate ecu based issues.

Dann

Bit of a left field option!
Disconnect the Idle Air Controller (IAC) connection and see if that overcomes the problem.

A number of NB8B's appear to have had issues with the IAC based on the info on the big forum.

Beat you mate lol.

Dann

NitroDann wrote:Have you tested the manifold for air leaks with car by cleaner. Have you tested the things connected to those hoses with car by cleaner? If you disconnect the IAC valve while the car is idling properly this will help you eliminate ecu based issues.

Dann

ive tried that, car will increase idle to 1500~ rpms and will not come down.

yep also tried carby cleaner on all the vacuum lines, inlet manifold etc. might have to scan the ecu for error codes?? car has lost low end response as well and running a little rich.

psi-mx5 wrote:ive tried that, car will increase idle to 1500~ rpms and will not come down.

yep also tried carby cleaner on all the vacuum lines, inlet manifold etc. might have to scan the ecu for error codes?? car has lost low end response as well and running a little rich.

Well maybe the idle screw is set wrong and/or a vacuum and/or the ISCV is faulty.

When a hot engine has the ISCV unplugged it should idle at the standard idle speed. If it climbs or dips when unplugged (or GND and TEN are shorted in an NA6 which puts the ecu into diag mode) then start with adjusting idle with screw. If that doesn't work then air is leaking into the intake. If your are certain that isn't happening, then inspect the ISCV. I've seen several where the entire problem was the gasket between the TB and ISCV. Replaced that and everything went back to normal.

G

psi-mx5 wrote:

NitroDann wrote:Have you tested the manifold for air leaks with car by cleaner. Have you tested the things connected to those hoses with car by cleaner? If you disconnect the IAC valve while the car is idling properly this will help you eliminate ecu based issues.
Dann

ive tried that, car will increase idle to 1500~ rpms and will not come down.
yep also tried carby cleaner on all the vacuum lines, inlet manifold etc. might have to scan the ecu for error codes?? car has lost low end response as well and running a little rich.

Base idle should be about 850rpm +/- 50rpm
There is a fairly good description on how to set the base idle at post 6 here
http://forum.miata.net/vb/showthread.php?t=405800
Another option is to obtain a throttle body complete with IAC (NB8A or NB8B) and swap it out!
Good luck

thanks for all your help guys, i think i fixed the problem... i think.

last night the idle was holding 1500 all the time so i parked it up and did some work.

i disconnected the battery, pulled the tb off, pulled the tps off and cleaned it, pulled every single electrical connection off (tps/maf/coolant/others that im not quite sure off) and contact cleaned them, put it all back together and... problem is gone.

driving to work today, idle sits just shy of 1k which is pretty normal for me, car goes better etc.. smiles all round!!

Disconnecting the battery also resets the OEM ECU.

93_Clubman wrote:Disconnecting the battery also resets the OEM ECU.

yeah i know, im hoping that its all solved, i doubt it but still hoping. also disconnecting the battery fixed my immobilizer problem as well... its a win win