idle issue: yes i have dug through tons of FAQs

[houstonh]

this isn't a complex one, I need more of an explination which should help me to resolve my issue.

1st off I have been told the idle on my car isn't that bad, but I still don't think it is inspection worth. I feel miss-fires and stumbles.

Now the question:.

What does it mean when I can barely open the throttle I mean barely.. and the car reacts like it has a vacuum leak (bouncing idle). I have also noticed when in nuetral.. I hit the accelarator then hold at any given interval the RPM's fade slightly when I pause at a certain point.

When I had these types of issue with my old integra it was because i f'd with the throttle screw.

This could certainly be the same, but I am curious.. could it be the TPS?
How does an engine differentiate a vacuum leak from intended induction of air? Is the answer "by providing fuel and spark"? I am not new to cars, but just trying to think a little more critically before throwing cash at the problem.

thanks in advance
Houston.

[rcko]

there is a bypass air screw on the AFM, but this is mostly for idle mixture control. there really isnt a way to screw with idle in the Motronic 1.3. The computer will just go angry trying to fix whatever is leaking or not reading right. a cheap way to ck is to measure the voltage signal from the o2 sensor with the screw all the way in then out. Then scew it back in into until you get a half way voltage of the range you measure for fully in and out

Get a can of carb cleaner and clean the ICV. I am guessing you already ckd for leaks... Get some electical cleaner and clean out the TPS. If you search here you might find the correct ohm output test and pin outs. I think it went something like open circuit at wot ot something like that I cant recall but it is posted here somewhere. These little gems get pretty filthy and a bath helps them out. Finally, I would clean the AFM.

Really the ICV is what basically tells the ECU whats going on with the idle air. My car rpms dip a little as you mentioned after holding rpms. My conclusion is that these E30s tend to have a slightly loopy idle and slow reponse throttle.

Where in DFW are you located?

[houstonh]

I'm in Frisco.

thanks for the response.


I have checked for leaks and had 3 different AFM's in there. One was bad.
I have checked for leaks, but I swear I can't rule them out. I am just wondering if there is something like the throttle stop screw that is off. (I think there is a throttle stop screw on these things)

I will clean the tps and go from there. Sounds easy enough.

[regis101]

High mileage cars ( yes, that means 150k and up ) tend to want and/or need a quick valve job. Just a lapping of the valve to the seat can get you out of the forest.

Also , try running the three different gas grades offered at the pump. You may find that it runs better or worse. Mine acts best with mid-grade.

Can't rule out that all three of the AFM's you tried had some type of individual quirk.

If It were mine, I'd give it a good tune up and take it to a mechanic with a scope and a sniffer. Much can be told while watching the scope.

Since most of your problems seems to be just off idle, my main tought is it may be getting tired. Meaning the valves aren't seating well. A vacuum gauge can provide a plethora of info once you know what to look for. These aren't used much anymore for diagnosis. I swear by them and have one installed in the three vehicles in our stable. If you do install one, even if just for testing, watch the needle movement at the off idle spot where you have the most trouble. My guess is that you'll notice a flickering needle.

just some thoughts

[PiercedE30]

Check the TPS. Easy to check and make sure it's good. It made need to be adjusted so that when the throttle is closed, the switch isn't telling the computer it is open.

[scabzzzz]

First thing I thought was replacing the throttle cable. Its almost guaranteed yours is stretched and shitty and you dont know what to compare it to. If its in bad shape or just plain old worn out, the butterfly wont adjust to the fine measurements of your foot and the cable. That piece is like 20 bucks. Guaranteed to give you better throttle response at LEAST.

[jlevie]

On a 20'ish year old car the probability of an intake leak from a cracked hose, bad, gasket, etc. is pretty high. While a gross problem can be may be evident from a quick visual inspection, more subtle problems require at least partial disassembly in order to inspect hoses and the like. And since a leak into the crankcase, within the brake booster, or into the fuel tank are possible intake leaks additional diagnostic work is required to rule those out.

If only idle was affected, an intake leak, bad/sticky ICV, misadjusted throttle/TPS or a bad TPS would be the likely causes. But since off idle operation is affected and there are misfires, the search for problems widens to include the fuel delivery system (do a pressure and FPR test), injectors, ignition system, timing reference sensor, and DME.

The first thing I'd do would be to rule out or find/fix any intake leaks. Including checking for leaks into the crankcase, fuel evap system, and brake booster. Then do a valve adjustment and ignition refresh (wires, rotor, & cap). Follow that by adjusting the throttle and TPS, verifying operation of the TPS, and checking the fuel delivery system. If that doesn't solve the problem you have to move on to the sensors that feed the DME (engine temp, O2 sensor, timing reference, AFM) or the DME itself.

[rcko]

All of the above are really good advices. I would follow them and just trouble shoot one system at a time. It will take a while but you will sort it out.

There is a throttle adjusting screw on top of the TB where the cable connects. The spec is basically close, some ridiculosly small feeler gauge number. Things that you do here will just cause it to idle faster... BTW it should idle at around 750-800.

CLean the stuff as suggested above, ck your valve clearance and go from there. THese are all cheap/free ck you can do.

Regis, you are the second person I have read recommending the use of a vacuum gauge. I need to read and learn more about these...

[regis101]

, you are the second person I have read recommending the use of a vacuum gauge. I need to read and learn more about these...

The best source for info would be an older Chilton's manual. They seem to have a tad more detailed info than some of the later version. Doesn't matter what make or country that it covers. Try the Public Library. Something from the 70-80's