So long story short I've been doing some much needed maintenance on my 2001 GS300. 203k on it, I've owned it since 194k and the previous owner probably never had the car serviced. Today I tackled the plugs and plug wires. Denso iridium twin tips @ .043 inches and Denso replacement wires. Slight pain in the ***, brittle plastic etc. Valve cover gaskets are leaking, pooled oil in the galley where the coils sit. Cleaned it all out though.

Got it all buttoned up and if fired right up, no miss, purred like a walrus. Let it idle and warm up, few revs all good. Shut it off, went and changed my clothes and proceeded to take it for a spin. Was doing good for a couple miles, then going up an incline at just under 3k I could feel a slight hesitation. Nothing harsh, just a drop in power for a split second. It will rev past that, all the way to redline, but I will feel that every so often. It feels like its always in the same two areas, 2.8k to 3k and maybe 4k or so. I can barely step on the throttle and it wont do it. Just with a 1/4 throttle or more.

No CELS or anything
Idles great
Takes off smooth and has noticeably more low end power.

If it had a constant miss, I would say I messed something up. But only in a certain rpm range? The car feels great everywhere else, so before I pull it all apart again I wanted to ask what everyone else thinks.

 

Did h changed air filter if it's real dirty it won't pull as hard when u hit the gas

 

No and I bet it's old as dirt, but like I said this is an abrupt loss of power not constant. I guarantee the fuel filter is the original as well. Again I did not have this problem before the plug and wire change, but it doesn't act like a plug or wire issue to me. If someone had a similar issue like a weak coil maybe or something like that, like at a certain load it just doesn't have the voltage to create a good enough spark?

Also, wouldn't the ECU see a misfire and throw a CEL? I can always hear/feel a misfire and I'm not getting anything through my exhaust (muffler delete) and it idles and feels smooth as ice when driving.

 

Could be a vacuum leak, I have a 300 but while driving the hose to the intake because loose and there was a very inconsistent throttle response with zero CEL. I could be completely off, but ys a very cheap and simple fix if that's he case.

 

You should get a new air filter and clean the maf sensor and throttle body, very easy cheap things to do yourself that could help

 

Well I took it out for another spin, issue did not happen one time. Drove it around for 15mins or so trying to make it reproduce the issue and no dice. Works for me

 

Make sure your battery connections are clean and tight.

 

I have the same exact mileage, and had a similar problem. I had a low idle and intermittent hesitation in the first half of the rpm range. Problem turned out to be a vacuum leak on the intake pipe. The resonator that hangs low, near the headers, had split at the seam; very easy to miss. Unmetered air was getting into the engine, causing a misfire. Might not be that since you have no codes, but food for thought in any event.

 

If the issue comes back I'll look into those things.