Slowed Acceleration - Corolland: the Toyota Corolla Forums

Guest PwnT

Well, my car has set up for at least 5 months with a warped head, burnt, and bent valves.. It was then sent to the shop for about 5-6 weeks. The head has been reconditioned, with new valves.. I get the car back and it hardly wants to move.. So the timing was advanced a little.. and it was better.. Someone told me that sometimes the valves have this wax like coating on them and it was probably just breaking them in, and it hasn't fully gotten the coating beat off yet, so the valves aren't going all the way up.. Well, I've had the car back for a while now, still not a lot of acceleration change.. When I floor it, it's like all the power just drains from the car, but if I keep it floored until I hit about, 25 mph, it's like you can feel a thrust of power, and then it goes fine from then on, except when you hit 2nd, it slows down a little more, but once it gets revved out, it boosts again.. The valves are still rattling a good bit, so, I'm thinking maybe it's because they didn't set the valves correctly to the shaved head.. I "was told" they had to shave the head by 20 thousandths.. So, like I said, I'm guessing maybe they didn't set the valves correctly, or maybe the timing is still off?.. But once again, the problem is poor accelleration which evolves into a boost of accelleration around 20-30 mph.. Any feedback would be greatly appreciated..

Need a bit more info - type of engine and car this is referring to.

Usual thing is the bent valves - as most Toyotas are the non-interference type of valve design. Some of the GE head models were interference type and could bend valves if you overrev or missed a shift. 20 thousandths of an inch is about 1/2 millimeter - not out of the ordinary for a resurfaced head.

Could be in the stage of needing to break in - could take a fee hundred miles before it starts to do that - assembly lube does take a little while to wash off in motor oil (usually within a few hundred miles) - but there is no "wax", so to speak, in there - but the valves would need an adjustment after the break-in period. Unlike a brand new engine - a "refreshed" engine needs a tune up and valve adjustment after the break-in period.

As for the lack of acceleration at low speeds - was it better or worse after you had some head work. If it was better after - then you have some other problem with the engine, ignition, fuel, or transmission with the car. If is was worse after the repair - look to the ignition timing, wrong valves in the head, valve overlap wrong, wrong camshaft, pulley is off, fuel managment problems, ECU problems (need to be reprogrammed after this type of repair - unless they used a thicker head gasket), and a few others. You could also have a combination of different problems going on here - need to get a compression test, volumetric test (head), ignition timing checked, check the air fuel ratio, check the outputs of all sensors and verify with the ECU.

Does this only do it under full throttle? Did you try backing off the pedal - when it starts to bog, let off slightly - does it accelerate less or stay the same? Smell any fuel? MPG better or worse than before?

Need some more info.

Guest PwnT

engine is 1.8L 4 cylinder, the accelleration was worse after repair.. when i floor it, it kind of bogs down at first, but up around 25-30 it boosts.. when press the gas slightly, it accells better..

Sounds like they screwed somthing up. I can't really tell you exactly what is wrong - since there are several probable points of error.

The main three are fuel, ignition, and induction.

You didn't mention a model year - but earlier Corollas have a fuel pressure regulator on the top of the valve cover, off to the side with a screw adjustment. Usually you don't have to mess with it - but some old school repair guys will open it up for some more flow (works for V8s, not really for 4 cylinders).

You mentioned that the ignition was advanced to help with drivability - that should indicate that the cams were probably off (timing). They have to make sure that the intake and exhaust cam gears mess together at the correct point.

If the valves are not set correctly, are oversized, or the seats are not ground down correctly - you will get some valve shrouding, which will really would sap the power.

Sounds like it is a timing and fuel / air issue - since it bogs when you get on the gas (floor it) - but is better if you give it less. Heve them redo it or take it somewhere else.

Good Luck.

Guest nomad17

I had bogging issues recently and it was due to a dirty MAF sensor. It was covered with gunk that apparently got past the filter. With all the work you had done I doubt it's that simple but worth a look.

Guest PwnT

ah, sorry about not mentioning a year lol.. its a 93'.. thing is, is that.. right when i got the car.. it didnt have as much power as it did before.. i was guessing it could be the cam not being adjusted correctly and/or valves.. i don't know if the MAF is working or not, because when i got the car, i made a make-do short ram intake.. and i forgot to plug up the MAF, well.. it really didn't seem to make a difference. I seen that it wasn't connected, so I connected and drove it.. then i disconnected and drove it.. and i didn't notice a difference at all. as for the overreving, i don't think that's it, because when i got it, i took it easy for a while.. for at least a few hundred miles.. after that, i was told the valve rattle should stop.. but it hasn't. and another weird thing i noticed.. when I got my car back, it was louder than before.. and now, for some reason, it's way more quiet.. than when i first had it.. when i had my car i took the resonator off, so there was only the muffler and the CAT.. so it was pretty loud, but now it isn't as loud.. i don't know what that could be.. it seems very odd to me, lol.. oh well.. thanks ahead for any information.

Guest PwnT

oh, and one other thing, i seen a mod that you put on the airflow sensor that's supposed to give you more HP. It was a resistor, if you know what i'm talking about.. what kind of resistor was it? I know someone with loads of resistors that looked like what I seen on ebay, but i dont know what exact kind it was.

That mod will trick the ECM in thinking it will get cooler air than it already thinks it is getting - sort of a virtual cold air intake. Problem is - that the effect will only work sometimes, under the right conditions - other times, will make less power. Loks good - but it is a total scam.

In your case, it will make the bogging problem worse. Since you tell the ECM that the air is cooler - it responds by pumping more fuel into the mix. Since you already bogged down - adding more fuel will only make the car run worse.

I don't remember for sure - but I think the 1993 1.8L used a MAP and an AFM sensors instead of a MAF sensor. In that case - using a DIY ram air intake will cause the ECM to learn an offset fuel curve. Might be worth a shot to install the OEM intake and reset the ECM (if you still have it).

Sometimes - disconnecting the negative battery terminal or pulling the ECM fuse/circuit breaker for a couple of minutes to clear out the short term fuel trim information - then driving it around normally may help. Worse case - if nothing is found to be wrong - you might have to resort to a stand alone A/F controller.

Good Luck.

Guest PwnT

well, the short ram never caused problems before.. so i'm just guessing, maybe the MAP is going out in it?.. i dunno.. but it does seem like it's getting too much fuel.. likes it floodin out whenever i give it gas.. but then its alright at higher speeds.. the other night, the valves real clattering loud as hell, now they're fine.. i guess that's because they havent been adjusted for the 2nd time. they're still hearable though.. even now, you can hear them at idle.. they arent real loud, but they aren't not noticeable.. im hoping it's just adjustment and not messed up valves.. but i don't know a whole lot about cars..