TVIS, not sure if tis my Culprit or not.

[Xenon676]

As i am not sure how to test the TVIS or what its operational parameters are, I am not sure if its my problem.

1985 MK1 - 4AGE n/a

My problem is this, in throttle I get sketchy response from the engine until about 2900 RPM. at that time the throttle response is what it should be. But, (LOL there always is a but) If I still get to much into throttle its response returns to sluggishness. In other words at 2900 RPM if the throttle is partially applied it accels very nicely. If i try and accelerate it even harder it returns to the slug state. If the TVIS is not the problem then I am almost sure its the throttle position sensor. But I'd like input from someone that knows more about the TVIS then I do. Anyone got some awesome advice?

[drewfuspx]

I am also having a problem very similar to this! I also have an 85' and have found that if I drive in this sluggish area for a minute or two I get an engine light until I either accelerate or decelerate about 200R.P.M.

I did check the code that I was receiving and it said that it may be a case of a dead O2 sensor, or clogged injectors, and prolly means it's running LEAN. I cleaned my injectors and that seemed to help a little bit but still running into the light. My personal next fix is to pony up the $$$'s for a new O2.

I'll be watching this thread with much interest. I feel like doing a swap now just to get rid of the sluggish-vroom acceleration!

[espguitarist33]

i don't know if it is...but i have an 85 o2 sensor for sale..and all the parts for the tvis system for sale...and injectors if their broke....and well whatever you figure out is wrong...let me know

[te51levin]

Originally Posted by Xenon676

Anyone got some awesome advice?

Yes! But it's not what you wanted to hear.

My awesome advice is this: get a shop manual and start diagnosing!

I don't mean to be difficult, but this is not something that happens commonly and has a common cause. If this was behavior that we saw all the time, we could give you some more specific advice. Unfortunately, though, there's no shortcut here. You're going to have to start right at the beginning; make sure that the ignition timing is correct (using the procedure in the BGB), make sure the coolant is filled properly (using the procedure in the BGB), and then start diagnosing, system by system.

There are a couple of dozen things this could be caused by - anything from water in the spark plug valley, to old or cheap (non-OEM) spark plug wires, to a weak or loose battery terminal, to a maladjusted or failed TPS, to a sticky or failed AFM, to an air leak between the AFM and throttle.

[espguitarist33]

and i have cheap used parts to fix any of that

[jsnod25]

and im having a similar problem with my 88 4AGE N/A... also a drop in idle to about 500 rpms on occation... and my temp guage is peaking almost as soon as i turn on the engine even though its not even hot yet (heater wont blow out hot air for about another 4-5 minutes).

[espguitarist33]

jsnod what kind of troubleshooting have you done so far? have you checked the coolant temp sensor? sounds broken

[te51levin]

jsnod25: You need to fill and properly bleed your cooling system immediately.

[YellowJacket]

Originally Posted by te51levin

jsnod25: You need to fill and properly bleed your cooling system immediately.

There is another one for you JSNOD25... And its from toyo master himself... that makes four people telling you to bleed your cooling system.
Aaron, he has a whole thread on this issue here -> Strange Behavior

Now back to the OP issue... unplug your TPS and see if the problem goes away.

[te51levin]

No question. Flush the system, put in a new thermostat, burp the system, drive happy.

I absolutely cannot stress strongly enough how crucial it is to use a genuine Toyota thermostat in a Toyota, but especially in an MR2. DO NOT use any other thermostat. They ARE NOT the same and they WILL NOT work anywhere near as consistently as a real Toyota thermostat.

[YellowJacket]

Originally Posted by te51levin

No question. Flush the system, put in a new thermostat, burp the system, drive happy.

I absolutely cannot stress strongly enough how crucial it is to use a genuine Toyota thermostat in a Toyota, but especially in an MR2. DO NOT use any other thermostat. They ARE NOT the same and they WILL NOT work anywhere near as consistently as a real Toyota thermostat.

You think the OP's throttle response problem is just his tstat? or were you making closing comments (good ones too) on Jsnod25's issue? (this confusion is what can happen when threads get hijacked)

[te51levin]

Well, it was mostly directed toward jsnod25's concerns, but on any MR2, or any EFI Toyota, it's a damned good place to start. It's one of those things that, like maladjusted valves or ignition timing, can throw everything else off.

There is little point in trying to diagnose a problem until we are absolutely positive - not assuming, but confirmed positive - that the fundamentals are correct. I am a hard-core stickler for double-checking the basics every time, before you try to root out any specific issues. This is especially critical on older cars, those that have not been worked on in a while, those that have been worked on by others, and those which you've only recently purchased. It takes a few minutes, but really, it saves a whole lot of people a whole lot of guesswork!

[espguitarist33]

amen

[Xenon676]

I do have the idle problem also my idle will occasionally drop to about 500 and sit there and shake the whole dang car, idling that low. This in addition to the throttle response problem that i started this thread for. Anyone know of a way to test the Throttle position sensor?

[YellowJacket]

Originally Posted by YellowJacket

Now back to the OP issue... unplug your TPS and see if the problem goes away.

^^^
Make sure you have bled air out of your cooling system as well.

[mr2_jake]

Procedure for TPS adjustment is in the BGB, or other equivalent manual... If you don't have one, here is a nice tutorial, with pictures!

MKI MR2 Write-ups

[PPiechocki]

my '85 had the same problems. unfortunately, my culprit was A LOT more expensive. my timing belt jumped a cog and it caused my motor to blow a hole in the side of the #4 piston. $1,800 performance rebuild. i'm in the process of re-installing the motor right now, and i'm taking the extra steps...new vacuum hoses, new radiator hoses, new t-stat. i'm hoping that'll clear up the problem.

[te51levin]

Originally Posted by PPiechocki

my timing belt jumped a cog and it caused my motor to blow a hole in the side of the #4 piston.

Huh? 4AGEs are non-interference, like almost every other belt-driven Toyota. What exactly was the failure?

[espguitarist33]

when i spun a bearing it jumped a cog...chipped the piston...and blew 2 holes in teh block....did it knock at one point?

[jsnod25]

ok, looks like i missed a bit since i posted. I didnt mean to hijack the thread, i just saw a post with a similar problem and wanted to relate... and as far as what have i done, I have burped the cooling system 2x, 1st time had a couple bubbles, second time no new air. I have changed the oil, oil filter, spark plugs and gapped them to 1.1mm also cleaned the MAF and the throttle body with CRC MAF cleaner, which ill ask a question about that in a second.

I can try burping/bleeding the cooling system... again... and even though im no expert, i dont think my cooling system is busted, just the tstat or the sender, sending the wrong temp to the gauge... and i also am pretty sure my tstat/sender temp problem is unrelated to the strange idle issue, maybe its not. But its also affecting acceloration too, though its not poping the check engine light.

Im sorry if i seem pursistant, and i do try everything that is reccomended to me to try, but so far no results in curing this issue. Only thing i can think of trying next is fuel supply, along with wanting to fix the temp issue. I must make clear, that despite the fact that the gauge is pegging immediatly after i turn on the car, i know for a fact that the engine is NOT overheating. My issue is that if ever it DID overheat, i wouldnt know because the gauge is sticking to the peg whenever im driving. So i just want to fix it for those hot summer days when im driving erratically and my cooling system does have a problem and starts overheating so i can turn off the car and fix it rather than drive it into the ground...

And as promised, when i cleaned the MAF, it was pretty clean, other than some white oxydizing inside... but the throttle body was horrid. It had black grease as black as black can be, and quite thick and greasy... is that just the EGR pumping exhaust back into the thing, building up carbon over the last 21 year? is that normal? should i take it apart completely and clean it thuroughly? or is that relativly healthy... i assume its natural, but not entirely healthy, and my CRC cleaner wasnt doing it good enough for me.

So i have 3 questiong.
1) How should i fix the temp issue (not overheating)
2) What should i do about a dirty throttle body and TVIS
3) Where should i start in the fuel supply to try and fix the idle issue Filter? Pump? Line???

i pretty much have the same issue as the guy who stared the thread, though the cause might be different, im just trying diligently to fix my problem. forgive me if you consider this hijacking, but maybe fixing my problem will help him fix his as well.

P.S.

I post in different subject areas that are related to my issue, because some people read other areas and not everyone read every area, so im just maximizing my reach of guru's in the forums. And im not some kid, though i might be to some, but im 27 years old, and really trying to learn about this car as much as possible. Im out there a few hours a day trying anything i can think of and anything you (the community) can think of, short of spening hundreds on new parts i cannot afford yet... So far i have spent hundreds on parts and tools and still not fixed the same issue ive been trying to fix since i bought the car, though everything i HAVE done, prolly needed to be done anyways.