Power kicks in after 5k rpm

[3rde30]

So I recently got my 3rd e30 an 89 325i but it's been almost 10yrs since I've driven one and I have a question before I hit the search bar
While driving I flows through rpms smooth but almost feels powerless and then all of a sudden at around 5500rpm it feels like it gets a huge boost of power,
My question is, is that normal operation or should I start looking in to doing some repairs?

[Eskie]

All the power is in the higher RPM’s on an M20 but it should be smoother getting there. Could be an issue with the TPS switch or air flow meter. Maybe even a vacuum leak.

Clean E30!


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[325e '87]

Yeah, my ‘89 is pretty smooth but I have a new tps and I know the afm is good, also the fuel pressure, clean injectors, clean plugs/wires/dist cap and rotor, O2 sensor, coolant temp sensor (2 wire for efi). And of course vacuum, mine was leaky at the brake booster but if you have a nice idle and cold start I doubt it’s a small vacuum leak.

Fuel pressure, lines, clean injectors, coolant temp sensor, and O2 sensor, filter and pump
Ignition stuff is wires, coil, cps, dist, batt
Air stuff is intake, idle control, vac lines, filter, afm

It’s a lot of stuff but then again it’s pretty simple to refresh most all of it whether it’s old or not.

[3rde30]

It idles fairly smooth plugs and wires are good did find a small vacuum leak on one if the injectors so I'll be replacing the orings on all and a few vacuum hoses that were cracked but not leaking since I'm gonna be in there

[ForcedFirebird]

Do a continuity test on the TPS. My money is on it being out of adjustment (or bad out of the box). The mounting holes are slotted and needs to be set before reinstalling the throttle body. Two of the three pins will be a dead short on a multimeter with throttle closed, all three should be infinite (all open) at any throttle input, and near full throttle the other two pins should be shorted. Loosen the screws on the TPS and adjust until the two criteria are met. Kind of a pain, but the screws cannot be reached with the throttle body installed, so this needs to be done on the bench.

The m20 has a three way switch, not variable voltage TPS. When the idle switch is closed, the ECU reads a small idle map (something like 4x4 bits), then there's a larger map for low part throttle, another large one for high part throttle (16x16 iirc), the the WOT map is a single 1x16 map where the ECU ignores the o2 sensor and adds a ton more timing. When in part throttle maps, the ECU is closed loop, so what you are feeling is the ECU ignoring the o2 after 5000 rpm. I have tested this on the dyno and the cars pick up ~15-18whp when there's a working WOT switch vs the TPS unplugged (stays in part throttle maps, and will run rich at idle speed).