GTR R34 Limp Mode

[steven7270]

So my car was recently having trouble starting on initial crank, I would need to feather the gas for it to start up but besides that it would start and run fine. So I clicked the idle air control valve (with throttle body cleaner) and cleaned the MAF sensors (with MAF cleaner). The start up issue was fixed and now the car turns over without the assist of the throttle, but the car is in limp mode and wont rev past 2.5k RPM. From what I understand the IACV would not put the car in limp mode, so I am to believe it is the MAF sensors, but it was running fine before and now I cant get it out of limp mode. I cleaned the MAF made sure the o rings were seated properly. Made sure the cables were plugged in properly, the cables also both read the same voltage. Does anybody know why this is or what could be causing this or how to get it out of limp mode?

[GTSBoy]

22 minutes ago, steven7270 said:

cleaned the MAF sensors (with MAF cleaner)

Has equal chance of cleaning an AFM and f**king an AFM. I think you can work out what happened.

22 minutes ago, steven7270 said:

but it was running fine before and now I cant get it out of limp mode

When the Hitachi ECU sees the AFM die and goes into the associated limp mode, then it will start and run just fine, because it ignores the AFM and just runs on idle maps that will do what it needs to get it going. But there is no proper load signal, so that's about all it can do.

My suggestion? If you don't want to go full aftermaket ECU, then get some R35 GTR AFM cards and some housings to put them in, in the stock location, and Nistune the ECU. Better to do a good upgrade than just replace shitty 40 year old tech with the same 40 year old tech.

[steven7270]

On 23/06/2025 at 12:39 AM, GTSBoy said:

Has equal chance of cleaning an AFM and f**king an AFM. I think you can work out what happened.

When the Hitachi ECU sees the AFM die and goes into the associated limp mode, then it will start and run just fine, because it ignores the AFM and just runs on idle maps that will do what it needs to get it going. But there is no proper load signal, so that's about all it can do.

My suggestion? If you don't want to go full aftermaket ECU, then get some R35 GTR AFM cards and some housings to put them in, in the stock location, and Nistune the ECU. Better to do a good upgrade than just replace shitty 40 year old tech with the same 40 year old tech.

if the MAF's were replaced should the car just turn on and get rid of the limp mode or does the car need to be ran for a while or reset before limp mode is gone?

[GTSBoy]

The fault code for the AFM should hang around in the ECU for a number of starts after new AFMs were fitted (and then disappear), but the ECU should start running properly immediately that it has working AFMs as inputs.

[joshuaho96]

On 24/06/2025 at 12:56 PM, steven7270 said:

if the MAF's were replaced should the car just turn on and get rid of the limp mode or does the car need to be ran for a while or reset before limp mode is gone?

As soon as the MAFs are replaced with ones that work properly, if the harness isn't ruined it should run perfectly immediately. 

[Predator1]

On 23/06/2025 at 1:14 PM, steven7270 said:

So my car was recently having trouble starting on initial crank, I would need to feather the gas for it to start up but besides that it would start and run fine. So I clicked the idle air control valve (with throttle body cleaner) and cleaned the MAF sensors (with MAF cleaner). The start up issue was fixed and now the car turns over without the assist of the throttle, but the car is in limp mode and wont rev past 2.5k RPM. From what I understand the IACV would not put the car in limp mode, so I am to believe it is the MAF sensors, but it was running fine before and now I cant get it out of limp mode. I cleaned the MAF made sure the o rings were seated properly. Made sure the cables were plugged in properly, the cables also both read the same voltage. Does anybody know why this is or what could be causing this or how to get it out of limp mode?

Oh dam. Thats going to be an expensive fix. Happened to me too. Ended up needing a big single and a seqy. Now it runs just fine.