88 F150 5.0 MAP sensor ?

'Some black smoke' indicates rich mixture - probably because with zero vacuum, the MAP is doing its job and telling the computer that the engine is at maximum load... If anything, seems that your experiment indicates that the MAP is working. This is a dumb question, but have you pulled the stored trouble codes? Ran self-test diagnostics? Will be much cheaper than throwing money on parts. In fact, you can do it yourself at a cost of a paper clip.

To test the MAP, unplug the ELECTRICAL connector, not the vacuum and go for a ride. If it is bad it will run better when unplugged. Plug and unplug with the key off.

"SSJ" wrote in news: snipped-for-privacy@localhost.talkaboutautos.com:

Common problem also with bad Fuel Pressure Regulator, see if there is gas in the vacuum port.

Thank you. I'll try thr paper clip test. I haven't done it befor, but have read many articles on how to do it. I'll follow the guidelines and see what I come up with.

Good plan and thank you. I'll try that and also going to try and read the codes via paperclip test as the Happy Traveller suggeted.

Thank you for the advice. I haven't considered the regulator. Also going to try and read the codes via paperclip method as Happy Traveller suggests.

how many miles on engine? is fuel filter replaced? air filter? i know it sounds dumb but years ago i worked @ a lumber yard had a truck that was so worn out (cat was also plugged) and vacuum was so low that it had these symptoms.