4AGE Not Running Right

[ahaav]

When warm, my AE86 idles around 800/900rpm, but it is not a steady purr. Instead it makes a low "buhbuhbuh" sound. Almost sounds as if it is cammed.

My car also jerks around a lot when I drive it, especially on highway speeds. Around 3000rpm+, the motor will cut out without warning and not let me rev any higher (cutting fuel I'm assuming).

I've adjusted the TPS as best as I can, and replaced spark plugs. Are these symptoms of a vacuum leak? I am thinking about blocking off the IACV altogether to get rid of all the extra hoses around there as well.

Thoughts?

[allencr]

What's the compression?
What happens when individual cylinders are disabled, by pulling the plug or injector wire?

[ahaav]

Compression test? I don't know much about compression but what should I go about doing to check that out?

What am I looking for if I disable a cylinder one at a time?

Thanks.

[yoshimitsuspeed]

What do you mean adjusted the TPS best you could? Either you adjust it right or you wasted time.

You can buy a compression tester kit online or at auto parts stores. Some autoparts stores rent or loan them out. If you aren't familiar with the process I'm sure googling compression test will get you more than enough info.

If you disable one cyl at a time and the idle drops the same amount on each cyl that is a good sign and means your issue is not cylinder specific.
If the idle drops less or not at all on one cylinder that means there is something wrong with that cyl like not getting fuel, spark or compression.


Have you checked ignition timing?
Cam/crank timing?
When were the spark plug wires, cap, rotor, air filter and fuel filter were changed?

Did you buy the car like this?
Has it always done this?
Did it just start doing it?

[ahaav]

When I first bought the car it seemed to be running fine and would idle around 1000/1100. I used a YouTube video to adjust the TPS, which entails using a feeler blade between the throttle stopper bolt and throttle valve mechanism, and twisting the TPS clockwise till it reaches the desired resistance reading on multimeter.

Spark plugs were changed yesterday. Wiring and distributor are relatively new. No idea how timing works on this engine. When I did timing on my VG30, I just made sure the belt marks were aligned with all the cams and crank gears.

[phanist]

what condition were you car running in when you first buy the car?. running nicely ? but just idling at 1.1k rpm? and rise from 1k to 1.1k? then you decided to adjust the tps? then it get worst? then that your problem there....the tps position incorrectly...

i don't think your idling at 1k rpm to 1.1m rpm have any thing to do with the tps...
put the fps back to the position it was at before you adjust it.. if your tps is position at a bad angle you would never be able to start up easily.... or not at all..
u didn't take your time to snap a picture of the tps position before you move it did you?..... find your self a buddy who can help u crank while u try turning the tps slowly to find the spot where your engine would be able to start...

i just have this a similar issue with my car.. not starting and one of the many issue is the tps.. and spark plug.. check your spark plug.. did you install the correct plug for your engine? look at the spec of the plug.....find a FSM it will help...you find the correct plug...

note i too try to set the tps tone as close to FSM and i have a very hard time starting my car up..... i guess you can try just turn the tps a little at a time and try to start up. if it doesn't start turn it a bit more... i guess...

Am i not an experience mechanic or a expert so don't believe me lol

[jrae82]

Sounds like a fuel filter problem. I had the same problem and I replace the fuel filter. It went back to normal. If ur still running a 20+ yr old fuel filter replace it now!!! Also check your ignition coil, wires, cap and rotor. Might need a nice little tune up as well.

[ahaav]

I'll check out the fuel filter next. No idea how old it is lol.

I drove the car for a bit today. It has been sitting for 24+ hours and ran fine. No jerking. However it always has a bit of trouble starting when cold. Doesn't turn over right away.

[phanist]

If the hard starting issue happen after you adjust your tps then you should be paying attention to that instead of digging into other things. Because while you start to remove other part again and you may mess more thing up... Just saying...

[yoshimitsuspeed]

When I first bought the car it seemed to be running fine and would idle around 1000/1100. I used a YouTube video to adjust the TPS, which entails using a feeler blade between the throttle stopper bolt and throttle valve mechanism, and twisting the TPS clockwise till it reaches the desired resistance reading on multimeter.

The exact reading isn't terribly important as long as it's relatively close to spec. You are adjusting it off of the idle circuit which is an on off switch. You want to make sure it triggers on (continuity) with the thinnest recommended feeler gauge and off (no continuity or infinity) with the thickest recommended feeler gauge.

[ahaav]

It was still hard starting before I touched anything. Only when starting it for the first time that day or something. I used .48mm feeler gauge.

[yoshimitsuspeed]

It was still hard starting before I touched anything. Only when starting it for the first time that day or something. I used .48mm feeler gauge.

Ugh, okay I'll open up my BGB.

Clearance between Lever and stop screw Between terminals Resistance
0 mm (0 in.) VTA - E2 0.2- 0.8 kll
0.35 mm (0.0138 in.) IDL - E2 2.3 kll or less
0.59 mm (0.0232 in.l IDL - Ez Infinity
Throttle valve fully VTA - Ez 3.3- 10 kll opened position
- Vee - Ez 3- 7 kll

You will want to do all the tests to make sure it's healthy.

For adjusting it you use two different feeler gauges as go no go gauges.

With the .35mm gauge you should get continuity.
With the .59 mm gauge you should not get continuity.
If yes then it passes.
If no then it needs to be adjusted.

[ahaav]

Thank you for opening your BGB!

I am going to replace the screws with hex bolts on TPS since they are in bad shape, and will adjust it then.

I hooked up a new intake today and capped the idle system. So if I'm correctly aware, the car will hunt for idle until at operating temperature right? (with IACV deleted)

It ran pretty good. I have yet to take it on the highway.

In the mean time, I also need a better intake hose, because the one I am using barely lets the filter clear the body. Can someone recommend a good silicone hose or something to connect the MAF to, and then the filter? I am using a cheap hose atm. And it doesn't need the idle air nipple since it is deleted as of now. Will a 2.25" inner diameter work?

[ahaav]

Drove it tonight and it ran like **** again. Jerking around everywhere, even at slow speeds. It's super frustrating. I guess the next step would be to check compression. T_T

[phanist]

was it running like **** when you just buy the car?....

[ahaav]

Not really. It only used to occasionally jerk on the highway.

[yoshimitsuspeed]

It's far from time to get frustrated.
It is time to take a slow methodical approach to diagnosing this.
First step is to confirm the TPS is properly adjusted. This is the most common cause for part throttle bucking.
One of the most next common is AFM so next I would test the AFM per the FSM. Also make sure the hose going from the AFM to the TB doesn't have an leaks, cracks or bad seals that could intermittently cause leaks.

After that it's time to go through the troubleshooting and diagnostics sections of the FSM. Some people find this overwhelming or something but it really is about the most efficient way you can troubleshoot issues like this. It will require being comfortable with the book and a multimeter.

[ahaav]

Thank you for putting things into perspective for me. New intake hose and such will be coming in the mail by the end of the week, so I will begin troubleshooting then. And let you guys know what happens.

[ahaav]

Hooked up IACV again. No apparent vacuum leaks. Now warm idles at 900rpm warm. Whenever I do wide-open throttle in any gear though, the engine stops pulling around 4000rpm. Why is this still happening ugh.

[jondee86]

Sounds like it is running out of fuel.... filter or pump maybe ?
Put your foor down and it hits X rpm then stops pulling, but if
you lift your foot it comes back to life ? Fuel cuts earlier in the
high gears than it does in the low gears ?

Cheers... jondee86

[ahaav]

I believe it's a failing pump. Cutting out at rpms under load points to this. I will be toying with the fuel sender unit since that it broken as well, and I will probably be messing with the pump as well.

[aukword1]

sounds like its misfiring...maybe a blown ignition wire or bad spark plug

[Uriel691]

So, have you changed the fuel filter yet?