Hey guys, I've been looking all over for answers but cannot find anything. I have a 93 vx completely bone stock, since I bought it it has had a weird pulsation under light acceleration/low rpm... when I say pulsation, imagine throttling the gas pedal on/off/on/off... I noticed it really only does it when hot (the hotter the worse), does NOT do it when the cel is on... no cel codes stored... while pulsation happens the speedo also dips at the same time... I have tried different clusters with no change, tried multiple and brand new vss... cleaned iacv, egr port, checked for intake leaks, cleaned injectors, checked mechanical and ignition timing, replaced spark plugs... any ideas would be great..

 

Does CEL work?

Last full ignition system tune up?

Have you tested the TPS?

 

CEL does work, I unplugged the vss to turn on the cel to see if the symptom went away. It did, thought it may be related to the vss so I bought a new one and the issue is still there. Figured the symptom must go away when in limp mode.

Spark plugs is all I've done so far, cleaned corrosion off cap and rotor and wires don't seem too old.

I have tested the TPS, did not see anything abnormal

 

Have you performed a valve lash adjsutment within the last 30k miles?
Last PCV valve cleaning or replacement?

 

I adjusted the valves about 1k miles ago after I replaced the rod bearings.

Haven't checked the pcv valve, although I am not sure how it would cause a pulsing idle? especially if it goes away with the cel on

 

What plugs? Properly gapped?

If you don't know how old the cap, rotor, and wires are, then replace them. It's part of good maintenance.

Did you check/adjust the ignition timing?

Old fuel filter?

Details?

 

Ill probably replaced the cap and rotor soon.

I checked mechanical and ignition timing, both were off so I adjusted them to factory spec (improved the issue but still present)

I haven't replaced the fuel filter (idk how it would make a difference) I understand if it were clogged it could be a lack of fuel but if I give it heavy throttle it works fine.

TPS, back probed (I don't remember which colors they were now) but had about .5v and closed throttle then slowly swept it open looking for any major spikes or dead spots, ended up at about 4.5v full open.

 

I honestly think the issue is in the distributor, I tested the coil and icm when it was cold and everything was fine but the issue arises when its hot

 

Reportedly, the VX is real particular about the oxygen sensor. The correct one is expensive but that is what you need. Some third party ones don't "lean burn" properly but they don't throw a code either.

When the CEL is on for most any reason, the engine doesn't try to lean burn.

Also make sure all parts of your engine system are truly VX, the lean burn system doesn't work right if you mix in ordinary DX EX parts.

If equipped, check EGR valve and passages for clogging.

 

Again, basic maintenance first. Also replace both the wires and filter and go from there.

 

Have you checked ground wire contacts?

Could be ICM/Coil they are always suspect for idle/load issues after the typical suspects are ruled out. Are the ICM, Coil and distributor OEM parts?

 

EGR is clear, I checked that.

I will see if I can test the o2 later

 

Everything looks to be oem, so could be age? just parts getting tired I guess

 

I have the same car, same problem. Mine was solved with a new O2 sensor. $160 on Amazon. Make sure you get the NGK 24300.

 

Did you test your o2 before replacing it?

 

Nope. I had already replaced the fuel filter, plugs, wires, TPS. Did more research online and was led to the O2 sensor. I'm sure it was the prob all the time. Also, the O2 looked original and probably was, since it took the force of 10 bulls to remove it. Car had 180,000+ miles. Time for a new one anyway.