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hemlocke
05-13-2008, 11:34 PM
1990 5S-FE, 160,000 miles, fairly recent tune-up (plugs, wires, cap, filters)
I drove to work, this morning, and when I pull up to the gate, the car starts idling down (under 600 RPM), then back up to normal idle, intermittently, and loss of power. I just checked the plugs, and they all show the car is running lean. Is the 5S-FE equipped with a MAF sensor, and could this be the culprit?

Okay, I finally found that the 5SFE has a MAP sensor, but does this function along the same lines?

The Captain
05-13-2008, 11:51 PM
sounds like the idle speed control valve.

hemlocke
05-13-2008, 11:54 PM
That would cause all 4 plugs to be lean, too?

Ads28
05-14-2008, 12:51 AM
yeah my car has also developed a nice surgeing idle.... cold start up its roughly around 1500rpm...n then itll go down to about 1000 after a couple mins of driving then after about 20mins of driving when i come to stop light and idle itll...will bounce from around 900, to 1800 continusly..havnt had time to trouble shoot, but from the sounds of the search id say idle speed valve, or coolent temp sensor?

Amaymi
05-14-2008, 01:28 AM
^Also check for vacuum leaks.

hemlocke
05-14-2008, 02:32 AM
Yeah, I just finished making sure there was no blockage in the fuel filter, checked for vacuum leaks, and reset the system. Still idles ROUGH at all speeds (I just put three new motor/trans mounts on it, and it is shaking.), but once it is warmed up, it will drop down and come back up to normal idle, and keep doing this. It never idles OVER stock, just drops under and acts like it will die. Under a load, it will get up to 70, just takes a little longer, but I'm afraid to take it anywhere, now, after seeing how lean the plugs were.

wraithlj101
05-14-2008, 03:30 AM
if its running lean then its a good sign that it is the map sensor. if the map sensor is not sensing the proper vacuum in the intake manifold, the ecm will not deliver the proper amount of fuel. i know a new map sensor from napa list price is $580....there is a way to check a map sensor in the haynes manual but i dont know it off the top of my head.
the iac runs roughly $275. but its just a valve, you can take it apart. if it is just siezing up, its easy to clean it. if the spring or piston is broken, then you will ultimately have to replace it.

Amaymi
05-14-2008, 04:08 AM
if its running lean then its a good sign that it is the map sensor. if the map sensor is not sensing the proper vacuum in the intake manifold, the ecm will not deliver the proper amount of fuel. i know a new map sensor from napa list price is $580....there is a way to check a map sensor in the haynes manual but i dont know it off the top of my head.
the iac runs roughly $275. but its just a valve, you can take it apart. if it is just siezing up, its easy to clean it. if the spring or piston is broken, then you will ultimately have to replace it.

A vacuum leak would also cause a lean condition. Vacuum leak can = more air in the manifold than the map is seeing and therefore not putting in enough fuel.

grayscale
05-14-2008, 03:18 PM
Just to be technically correct here-
The tittle of your thread is mass air flow sensor, or maf, which is incorrect.
You're referring to a map sensor which is a manifold absolute pressure sensor.

It's most likely your iac and probably not your map sensor. Easy test, get out in the road and try to accelerate really hard. If it stumbles when you try, it may be your map but not definitely. The bgb says to check your resistance on the map sensor to test it. I don't have mine on hand but I'll get it for you later if some one else doesn't.

hemlocke
05-17-2008, 04:21 PM
Yes, I had figured out before your post that the 5SFE had a MAP sensor.

I tested the IAC valve, and it seems to be working okay, and I have not found any vacuum leaks, so now I guess I will check out the MAP.

Lagos
05-17-2008, 07:31 PM
You have a vac leak.

hemlocke
05-18-2008, 01:40 AM
Okay, so I replaced every vacuum line except the ones marked #1 (EGR-VM) and #2 (No clue), but it has made a small difference, along with completely cleaning my throttle body and IAC, but it still isn't quite right. I'll crawl underneath it tomorrow and get those other two vacuum lines.

Could my canister be bad?

alltracman78
05-19-2008, 10:17 PM
You have a vac leak.

Stop being an idiot.
This is 100% incorrect. A vacuum leak will NEVER ever ever cause a low or rough idle with a MAP sensored ECU.
You have posted it several times [that I've seen]. Every time I see it I correct you, but it doesn't seem to sink in.
Every single time you post this you propogate misinformation.

THIS is what a vacuum leak will cause with a MAP sensor.

yeah my car has also developed a nice surgeing idle.... when i come to stop light and idle itll...will bounce from around 900, to 1800 continusly..havnt had time to trouble shoot, but from the sounds of the search id say idle speed valve, or coolent temp sensor?
Check for vacuum leaks before you look at the IAC or ECT sensor.
That much of a surge means it's probably a relatively large leak [if that's what it is].



A vacuum leak would also cause a lean condition. Vacuum leak can = more air in the manifold than the map is seeing and therefore not putting in enough fuel.
This is also incorrect.
A MAP sensor reads pressure, not flow.
If you have a vacuum leak into the manifold, it will increase manifold pressure. The MAP sensor reads manifold pressure, and will see this, at which time the ECU increases fuel. But because the sensor is reading MORE air than what is actually flowing into the engine [remember the TB is still closed; and this will only happens at idle], it runs rich, and the ECU leans it out. Then it richens it again because of the MAP reading. This is what causes the surging idle.

If you are in fact running lean the first culprits to check are the O2 sensor and the MAP sensor.
FYI, even if they pass the tests in the BGB they can be bad.

Ads28
05-19-2008, 10:29 PM
yeah ive checked and havent found any leaks to my knowledge, the surgeing doesnt happen very often, and now a new thing thats started (sometimes, none of this happens constantly its hit or miss)...is on wat should be a cold start up, the idle is down around 900, like a normal op temp idle, yet the engine is cold

hemlocke
05-20-2008, 12:40 AM
Nailed it in one, Alltracman. The guys at the parts store dissuaded me from getting one, to begin with, because they said that when O2 sensors go bad, they always go rich. I should have had my reasoning cap on and called BS, so I feel like a tool, now.

Ads28
05-20-2008, 11:25 PM
http://www.youtube.com/watch?v=WynPbEPhD3U video of said idle problem, went for a cruise last nigh and was all good, until 20 mins at a corner she decided to act up then quick lil boot and the surge went away, then next stoplight the idle was back to 900-1kish

jgcox6
06-11-2008, 10:23 PM
i have heard that a quick check for the map sensor...is to tap it with like a screw driver handle...with the car idle...and see if it trys to stall or idle rough....just a quick check..if it does it is bad...