Won't rev past 2,000 RPM and the MAF is good.....what else to check??

[goyal99]

Hello to allOn a 1990 NA Automatic with 150K miles the engine will NOT rev above 2,000 to 2200 RPM no matter what I do to the throttle cable or gas pedal.....The tach inside stays at around 2K RPM mark and the engine does not rev any higher....The car starts and idles fine with no apparent fuel issues...I also changed the fuel filter recently.

I've read in here that a bad MAF is usually the problem so I swapped it with a good working MAF from another '90 300ZX (Auto) and it makes no difference in RPM.....I checked all the vacuum connectors and they appear fine.....I checked ALL the coil packs and the spark plugs they all seem fine as well.

No ECU codes present - diagnostics return a 55 value (no malfunction)....

Is the TPS sensor the same as the THROTTLE Valve Switch as referred to in the FSM??

Besides the TPS sensor is there any other possible cause to this low RPM issue??

Best regards......Bill


Modified by goyal99 at 5:34 PM 6/22/2009

[Chrispy300]

Have you hooked it up to consult yet? Checked the readings that the ECU sees?

I still reckon it is AFM related, what condition is your plug in? Have you got continuity between the AFM and the ECU?

[goyal99]

Sorry but I don't have CONSULT tool.....I only have access to volt meter and regular tools.

Like I stated earlier changing the existing AFM (MAF sensor) with a good one did not solve the problem....I know the AMF (MAF) was good because it came from a good running Automatic 300ZX.....The condition of my plug is good and all the wires are fine....I cleaned all the plug contacts.

WHat pin do I check for continuity between AFM and ECU??

[evildky]

have you checked for codes? and the TPS test is detailed int he FSM which is the next lilely culprit

[goyal99]

Thanks for your suggestions....

a) there are NO ECU codes stored....I got a 55 (No malfunction code).

b) I just finished checking the resistance values for the Throttle Sensor (as per FSM EC-181) and they appear to be within specs:

- completely released reading of 1.33 KOhms ( FSM says approximately 1K Ohms) - partialy released reading of 4.6 KOhms (FSM says between 1- 9 KOhms)

- Fully depressed reading of 9.25 KOhms (FSM says approx 9 KOhms)

So if I'm reading those resistance values correctly for my Throttle Sensor then it appears to be within specs.....I cleaned the contacts and connectors well and put dielectric grease.

So what else to check?? any ideas ?? still the engine will not rev passed 2,100 RPM even with throttle fully depressed.


Modified by goyal99 at 5:32 AM 6/24/2009

[goyal99]

Has anyone have a good procedure to check the MAF sensor ??

Which pin on the MAF sensor communicates with the ECU??

Regards

[venomizzy]

goyal99....did you ever figure out what the problem was?? I'm having same problem with mine. Please share.

[z31beastturbo]

I have done everything you have with no success. I've had this issue for over a month. If anybody figures anything out please email me at [email protected]. I'll do the same. Thanks guys

[venomizzy]

On mine it was the coil pack, one of the coil was bad, changed all sparks as well. Car was running on 5 cylinders before. Hope that helps