95 240sx w/ poor idle and part-throttle stumble

[Maximum Velocity]

Stock KA24DE automatic with Injen short ram, cat-back exhaust, cat and egr delete. The problem started (coincidentally?) after it blew an upper radiator hose loose but did not overheat. The car now is hard to start (much harder when it is cold) and will only accelerate if you SLOWLY tip in to the throttle. Any mild/ aggressive throttle results in total loss of power with the car almost dying. When the car is in neutral, if you keep your foot in it, it will clear itself out at higher rpm and rev fine. When it is missing, the exhaust note is very deep and the car almost acts like it is hitting a rev limiter. If you gently apply the throttle in gear, it accelerates fine all the way up to 80+ mph without hiccup. When the car was misfiring under hard throttle, small bits of melted cat came out the exhaust (which is why it has a test pipe now)!

Here's what I've done: new plugs, cap/rotor, fuel filter, fuel pump, IAT, TPS, ECT.Checked for spark, fuel pressure (checked regulator too), o2 sensor readings, timing (verified by scanner and adjusting the distributor), compression (175ish across all 4 cylinders). Checked for vacuum leaks (audibly and with carb cleaner). Cleaned the throttle body on the car.I have swapped MAFs, cleaned the IAC and bench tested it (it moves).On the scanner, everything seems to check out. Only ocassionally will it throw a EGR solenoid code or an IAT code.

The only things I can think to do next: pull the injectors to look for leaks, check MAF grounds...Any ideas?
Modified by Maximum Velocity at 7:55 PM 2/21/2007

[dkdeleon68]

check MAF and wiring.

[Maximum Velocity]

Swapped the MAF with no change. The Scanner doesnt show any codes and looks like is reacting fine. Also changed wires and the IAC.

[rogoman]

Check the TPS and it's harness connector; especially the connector pins for any oxidation. The TPS is located in the same area where the hose blew out.

[Maximum Velocity]

Thought of that...put on a new TPS sensor, connections look clean, and it acts fine on the scanner (no jumping voltages or dead spots)

[180fan]

what are the voltage readings on the tps?

[Maximum Velocity]

what are the voltage readings on the tps?

TPS shows 0.4v closed to 3.92v WOT

Only persistent codes are P0400 EGR problem, P1400 EGR solenoid....the EGR has been blocked off and removed.

Other thing I noticed is the wires to the knock sensor at the connector by the TB look frayed (insulation is cracking off). No knock sensor codes though. Although when the car is sputtering badly, timing drops off to 0deg and sometimes is retarded. I'm just not sure if this is problem or just a symptom.

[boriquaS13]

Just a question did you change the cap and rotor before the upper hos blew or after. Because if it blew and coolant got into the distributer cap your car is not going to run good. So double check that and good luck.

[Maximum Velocity]

Cap and rotor were changed after the hose blew. No sign of water in the distributor or in the boots for plug wires.

[boriquaS13]

It is possible that your car is leaning out under hard accel but has enough for light accel. Does it sound like it backfires through the intake at all? Did you ckeck fuel pressure and volume? I have seen where you can have good fuel pressure and not enough volume so check that. Post up, lets see if we can fix this problem.

[Maximum Velocity]

Figured it out, appears to be either chain stretch or a bad tensioner. Ignition timing, which I verified by scantool, was way off. Had to restab the distributor 1 tooth off and max the timing adjustment back. Car runs like before. The only problem I have now is an idle surge....

[boriquaS13]

Sounds like you need to change that chain if you ever want to get it to run right. Are you sure you didn't jump a tooth on your chain? What is your timing set at? If its really advanced that would cause a surge wouldn't the ecu try to overcompensate for the to advanced timing? On the scanner can you see timing advance, is it jumping around more than it should?

[boriquaS13]

Oh and btw if it was that far out that you had to restab your distributor 1 tooth thats about 10 to 15 degrees of ignition timing correct? It really sounds like your chain jumped or it is really stretched.

[Maximum Velocity]

Yeah, the car has had typical start up chain slap for a LONG time. It needs a new chain and tensioner....