Engine Tach goes to zero,engine goes to idle on 87 GT

[Hogtown]

I have an 87 Mustang GT that’s driving me crazy. When driving the tach will go to zero but the engine keeps running but goes to idle. It doesn’t matter where the gas pedal is ,then the tach comes back and it runs fine for a short time and then it all happens again. This car has a list of new parts starting with computer, complete new distributor, wires and plugs, map sensor, coil, clutch switch, ignition switch, coolant sensor. The car is all original except for cat back. It does not have the Maf sensor. We’ve also cleaned all the grounds and replaced the battery cables. There are not any codes. It also has a new pigtail on the TFI. It does seem like if you push the clutch in it will start working again. Any suggestions will be appreciated

 

[Hogtown]

Any ideas ?

 

[General karthief]

Can you check for codes?

 

[Hogtown]

Yes I checked and no codes

 

[General karthief]

I find that suspect (the no codes thing), did you get 11 (all clear code)?
Test the tps, it should read below 1.0 at idle, open the throttle slowly and the numbers should rise smoothly and not jump to zero,
To diagnose this correctly you should go to the 'surging idle checklist ' you can find it in the technical/how to thread in the 5.0 tech forum.
I am leaning towards a wiring problem.

 

[Hogtown]

I’ll check the codes again And check the tps . Could the tps make the tach go to 0

 

[General karthief]

I think not. Tach wire is on the coil I think.

 

[Hogtown]

Still no codes. Switched new distributor to old one and now we are back to original problems. the tach no longer drops to 0. When pushing the gas pedal it won’t rev up and then starts bucking when going down the road. It will free rev. Does anyone make a good quality distributor ?

 

[Hogtown]

DUI distributor from summit fixed it. It’s running Thanks for the help

 

[jrichker]

Yes I checked and no codes

No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

 

[Hogtown]

Just got back from a trip to Tennessee from Pennsylvania. We also did the tail of the dragon. The car ran flawlessly the whole way.