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high idle; valve job, pistons, rings, low vacuum, idle 2000 rpm
Topic Started: Dec 14 2011, 03:06 PM (1,519 Views)
narftroz
New Member
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so i have a 93 vert that i just did the valves on. replaced them all and replaced the pistons, rings and rod bearings. runs great but as soon as i hook up the map sensor it jumps up to 2000 rpm. there is also a flat spot just at the point where you come off acceleration and drive a steady speed. the vacuum is low at around 12 psi. i am pretty darn sure the cam is timed right. i think there must be a vacuum leak but i cannot find it. when i plug the iac it makes little difference in idle speed. cleaned the egr twice.
please give me some suggestions to try..... thanks.
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crankcase


Check your idle system, either the ISC or IAC depending what system you have. My 93 base uses and IAC. When you take off the silencer (muffler like think, right off air filter, about the size of a D cell battery) you can hear the IAC motor chuging along. Soemtime the spring in the plunger breaks or the hose cracks or is not hooked up ect.

Glad to see you use a vacuum test. This is a very informative test procedure that people should use more. You may have a leak in you intake manifold, or the gasket under the trottle body where extra air is getting in. You can check this by running a little propane (non burning) from a tourch around these areas and see if it changes the idle.
Edited by crankcase, Dec 14 2011, 03:43 PM.
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narftroz
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if i completely plug the iac the idle drops from 2100 to 2000, so i think it is mostly working. the only thing that lowers the idle is disconnecting the vacuum from the map sensor. i have tried both soapy water and wd-40, i am leery of propane for this test, i have caught 3 vehicles on fire in the last 6 months so i want to avoid that one.
i also replaced the map sensor with a known good one off the same year geo, no change.
oh and compression is 200 on all holes, just in case anyone was wondering.
i also disconnected the vacuum brake booster and no change.
if this car was running on 1 cylinder from the previous owner and they didn't know what they were doing, could they have adjusted the idle up fast by the screw?
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crankcase


If I remember correctly, and this is really winging it, if the booster line is disconnected it shold about kill the motor???

That does not really jive with low vacuum, but something else may be comming into play.

It is very comon for the booster line to get clogged up (usually causes oscillating hi/low idle ), so it might be worth checking anyway.

Also check the small coolant lines going to the throttlebody, it is very common for them to get clogged up. The sensor never gets to warm up temp., so the car keeps idle high trying to warm up the motor.

As far as relation to the MAP, I can't remember, I will have to go study.
Edited by crankcase, Dec 14 2011, 05:16 PM.
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narftroz
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i didnt just disconnect it, that would be a big leak, i plugged it to make sure it was not leaking.

checked lines, not plugged, get warm real fast as well.

thanks again.
T
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Scoobs
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did you pull the tbi off? could be your tbi base gasket
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crankcase


Narftroz,

Sounds like you've got the situation in hand, but on the booseter I assume you see a change in idel with line pluged vs unpluged (as it should be).

You've probably done this, but carefully check all vac. lines (don't overlook hard to reach ones), check all electrical connectors, listen for sucking/hissing sounds. This is likely where the problem lies unless something was broken during the servicing.

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Alpine
1020cc G10 GOML

could you have put the throttle cable on to tight?
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clarkdw
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You have IAC instead if ISC if I read your posts correctly. That means you have an idle speed adjusting screw going in to the side of the throttle body. Start off with the simple thing of trying to lower your idle using that. Make a note of how much and which way you adjust so you have a baseline.

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narftroz
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Steved82971
Dec 14 2011, 05:32 PM
did you pull the tbi off? could be your tbi base gasket
no i did not do this yet. i may try that next. i blocked off the egr just to make sure it wasn't that. and it made no difference in the fast idle.

i have replaced all the vacuum lines including the non metal vacuum brake booster lines.

i will try the idle screw next just to make sure, but it idles at the perfect speed when i don't have the map sensor plugged in. if i unplug either the vacuum or the electrical connector it idles down to 1100 or so, without changing anything. is it idling up by increasing gas to the injector?
i have no codes, but could my computer be bad?
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narftroz
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Alpine
Dec 14 2011, 05:58 PM
could you have put the throttle cable on to tight?
good idea but i set it to factory specs on the play. and there is some play. again, it idles perfectly at 1100 or so in neutral, with the map sensor unplugged.
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narftroz
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clarkdw
Dec 14 2011, 07:59 PM
You have IAC instead if ISC if I read your posts correctly. That means you have an idle speed adjusting screw going in to the side of the throttle body. Start off with the simple thing of trying to lower your idle using that. Make a note of how much and which way you adjust so you have a baseline.

yes it is the iac, idle air control, which seems to be working correctly. and without doing anything to the idle screw, it idles perfect if i simply unplug the map sensor.
once again i have replaced it with a known good one from another vehicle, and it made no difference.
perhaps it is a bad computer?
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clarkdw
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narftroz
Dec 14 2011, 09:28 PM
clarkdw
Dec 14 2011, 07:59 PM
You have IAC instead if ISC if I read your posts correctly. That means you have an idle speed adjusting screw going in to the side of the throttle body. Start off with the simple thing of trying to lower your idle using that. Make a note of how much and which way you adjust so you have a baseline.

yes it is the iac, idle air control, which seems to be working correctly. and without doing anything to the idle screw, it idles perfect if i simply unplug the map sensor.
once again i have replaced it with a known good one from another vehicle, and it made no difference.
perhaps it is a bad computer?
Check carefully that all the sensor connector pins and the grounds on the intake manifold are really making good contact.. Check all them, disconnect your battery and touch the two cables together to allow the ECM to reset and try it again.

Very unlikely that it is the ECM
Edited by clarkdw, Dec 15 2011, 01:44 AM.
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crankcase


You said you have low vacuum; I would check that angle (what is your reading). You said your hoses are good, so the intake manifold would be a logical thing to check. If you decide to check with propane just have a fire exinguisher ready.
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narftroz
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clarkdw
Dec 15 2011, 01:42 AM
narftroz
Dec 14 2011, 09:28 PM
clarkdw
Dec 14 2011, 07:59 PM
You have IAC instead if ISC if I read your posts correctly. That means you have an idle speed adjusting screw going in to the side of the throttle body. Start off with the simple thing of trying to lower your idle using that. Make a note of how much and which way you adjust so you have a baseline.

yes it is the iac, idle air control, which seems to be working correctly. and without doing anything to the idle screw, it idles perfect if i simply unplug the map sensor.
once again i have replaced it with a known good one from another vehicle, and it made no difference.
perhaps it is a bad computer?
Check carefully that all the sensor connector pins and the grounds on the intake manifold are really making good contact.. Check all them, disconnect your battery and touch the two cables together to allow the ECM to reset and try it again.

Very unlikely that it is the ECM
ok so i checked all the connectors and they look and act like they are making contact. they all make changes in the running of the vehicle.
when i disconnect the temp sensor plug on the tbi, it actually idles up.
so where i am at is here.
1. vacuum only at 12
2. compression over 200 on every cylinder
3. checked mileage on last tank and it was 19 mpg
4. bad flat spot when going from acceleration to steady speed
5. replaced all vacuum lines
6. no codes
7. no external vacuum leaks found by wd-40 or water.
8. Idles at 2100 in neutral with everything connected. if i disconnect the MAP sensor it goes down to 1300.

next steps are to
1. double check heater lines in TBI for clearness
2. triple check valve timing
3. Check TBI to manifold gasket.

do whatever else you guys suggest!
Help.
I am getting half what i should, hell i could drive a super duty diesel and get better than that.
T.I.A.
Tim
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