extremely bad gas mileage

[aceof07]

guys help me out here, i'm getting about 100 miles out of a full tank of gas and by searching i found some of u get about 3 to 4 times that. i also have black exhaust at idle and also when i floor it. the engine shakes a lot at idle. what i've heard of so far is of course the coolant temp sensor,o2 sensor, possibly MAF(just got a new one tho), injector leak, maybe a vacuum leak? any one have any suggestions?

[aceof07]

oops i forgot. i have a 91 240sx 5 speed. sorry you guys. only has intake.

[Jasong]

It could be all of the above. Plus needing a tune really bad also a bad fpr.

[aceof07]

i have to add that the top engine was cut by the stupid engine fan. i only put the engine harness together with with some electrical tape but the bad thing is that i can't look up codes on my ecu to see if it can read all the sensors. i do know it was read the maf some what because it will let me go beyond 2500. any ideas now?

[apex760]

if u got an autozone up there they lend u their code reader u justleave a deposit an get it back when u give the reader back

[aceof07]

good point i'm about to try that.

[aceof07]

i just regrounded the maf the car no longer makes black smoke at idle and idle is also very stable. i still need to see what my gas mileage is now.