Question about 1990 Geo Tracker

1 Answer

Why is the engine running erratically?

My tracker started running erratic the other day it would not run without pumping and revving the engine,the diagnostic code shows map sensor. i saw where a vacuum leak or fuel problem could cause this code so I installed a new fuel filter and also pulled the throttle body and put new gaskets on the it and replaced some deteriated vacuum hoses, also I installed new pcv valve, now it sometimes misses at idle or speeds up to around 3000 rpm's at idle and then starts running rich and smoking bad. thanks for any help you can supply. JR

Posted by on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Geo Master
  • 20,706 Answers

The map sensor fail means (DTC code not stated sadly)
mean the voltage is stuck at 5v or 0v.
the ECU never lies about this, ever.
the ECU enters FAILSAFE mode , in this case. (limphome)
and runs rich has heck , horrid rich, misfires.
RPM limited
idle controls disabled.
and retarded spark timing.

pretty much worst of the worst for EFI ops.
all you need to do is post the DTC error. and all that is what matters.
new MAP time, or fix the vacuum hose. its clogged? cracked.
make sure the vacuum leaves the intake manifold (sucks) and
makes it all the way to the MAP on the fire wall and that the
tiny filter(check valve?) inline is clogged, (blown through it)

This is a G16A ENGINE, With an ECU that does not create or control spark, (old style distributor with mech, and vac, advance)

DTC 31 or 32??????????????????????

if vacuum line is breached to map , the vacuum is not 0" HG
the MAP outputs 3.9V

the ECU trip points i do not know. but
above 3.9 or below .5v it will trip... somewhere,

here is very good map , graph

all testing of it is here

with photos and how to back probe it with an volt meter.

Posted on Apr 29, 2015

Testimonial: "thanks for the info I will test asap. the obd code is 32, if any more info please respond."

  • 5 more comments 
  • _-__-___-_
    _-__-___-_ Apr 29, 2015

    in pure theory , an engines with horrid bouncing vacuum can fool any MAP sensor. (true on most cars made) so we always, (map fails) check vacuum first. with a meter. (gauge) 19" vacuum is normal at idle. not bouncing like a kid on a pogo stick. (ever change out the cam belt?)

    EFI systems cant run dead engines.
    or say one with cylinder 1, intake valve burned to crisp. see? that is because it makes the MAP go NUTS

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    pressure is too low 32DTC. so measure the green wire, pin 2. on the map. I think them mean that pin 2 is low voltage near 0volts, (a dead sensor) the correct voltage key , no started is 3.9v. that is the first check of any map sensor, keyon output. easy huh? just one check. and big clue. got a volt meter? any will work.

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    keyon, not started,pin 2 is 3.9V just like the graphic in link 2 shows.....

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    keep in mind the MAP is just vacuum gauge so the ECU can calculate air flow INTO the engine, so it can match FUEL to AIR flows. that is is Prime job, non trivial. if the map works, it will match the shop vacuum gauge attached. see? it's a simple analog, sensor, and linear, in actions. making it easy to test with simple tools. (volt meter)

  • _-__-___-_
    _-__-___-_ Apr 30, 2015

    when fixed, you will get back 28mpg again. imagine that.!

  • _-__-___-_
    _-__-___-_ May 01, 2015

    my guess, (tools in pocket) map connector fell off, or was broken at last engine pull (or map bad due to same reasons)
    maps almost never fail, only seen one, due to crashed at engine pull. (cracked)
    the code you see usually means , map dead. or not connected.

  • _-__-___-_
    _-__-___-_ May 01, 2015

    the voltmeter checks are supper easy.
    backprobing, skills?



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Check engine light does not function. aldl also will not work.diagnostic connection

Year/make/model? If no check engine light, look for a blown fuse to start. Without knowing what vehicle you have it is hard to supply information.

Jul 18, 2015 | Cars & Trucks

2 Answers

My '04 blazer has been revving erratically when I start it. Goes back to normal after a couple minutes of warming up, but when I drove without the warmup it was revving up on its own even when I h

I had an 04 blazer. There is an undocumented problem with leaks in the intake manifold. The original gasked was low quality. I would expect that you have a vacuum leak in the intake manafold. My problem was a coolant leak. Replacing the manifold gasked fixed it.
If not this, make sure you do not have any creaks or opening in the air hoses that fed the throttle body.

Apr 14, 2013 | 1996 Chevrolet Blazer

1 Answer

Service engine soon light started flashing then started to idle erratically

It sounds like it could be the o2 sensors, the mass air flow sensor, or the idle air control valve, take the vehicle to your local auto parts store and have them connect their scanner and pull the codes.

Jan 30, 2018 | 1998 GMC Sierra

1 Answer

Engine runs in idle +/- 2500 rpm

Without checking your car physically, its not possible to give you any idea what it could be or not

Dec 10, 2017 | 1999 Peugeot 206

1 Answer

My Chevy 2500, 2001 runs rough when it cold outside

It can be issue with low fuel pressure,the fuel pump is getting old both needs to be checked.Also get the IAC valve checked.
Go through the related help links with similar problem,it may help:---
Click the links below:---
Engine Idles Rough and Dies?

van idles rough?

runs lean and idles rough?

Car still runs Rough after tune up?

2006 kia rio runs rough

Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

Rough idle, staling and Erratic shifting?

These details will help.

Nov 06, 2012 | Cars & Trucks

1 Answer

Orange Engine Light turns on and off (Honda Civic Luxline 1.5 1999)

take the car to a part store they will run a scan for free

Jul 24, 2012 | Cars & Trucks

1 Answer

I have a 2007 ford ranger, 6 cylinder. I drove

The oil pump may have gone bad. Involves dropping the oil pan and replacing the oil pump, check the pan for any metal peices.

Mar 06, 2010 | 2007 Ford Ranger FX4 Off-Road

1 Answer

Heater comes on and go off when it wants to.

What you're likely referring to is the blowing air starts and stops erratically. Since the heater uses heat circulated from the engine, if the air is constant and the heat comes in and out then that's a different issue.
Firstly, if the airflow starts and stops, you'll find a loose connection between the the fan switch and the blower itself. If the connections are sound, then look for a loose ground connection to the blower. If all electrical connections are good, and it still starts and stops erratcially, then it's time for a replacement blower.
Secondly, If the air is constant and the heat comes in and out, the the options are a faulty water pump or partial blockage in the colling system or heater core. If the water pump is failing and working erratically, then when the heat dissipates in the cabin airflow (it has used all the heat in the heater core and no circulation to replace the cooled water with hot water) the dash temp gauge should start to climb, indicating that the coolant is no longer circulating, the heat has left the heater core but the engine is not being cooled. You'll need to replace the water pump. If this is the case, take care of this ASAP as you run the risk of a an engine overheat.
If the dash temp gauge looks normal, then you're likely looking at a partial obstruction in either the cooling system or the heater core that blocks the flow and then works its way loose erratically. Limescale and crud buildup in your cooling system (especially in a 15-ys-old car) can cause this when flakes of buildup brake loose from the walls of the larger channels and get caught up in the smaller ones. Your local parts store will have additives to clean out the cooling system, but if they don't work (they can only do so much) then you're looking at a professional cooling system flush. If the issue persists after that then you're likely looking at a heater core replacement.
Also check to see that your a/c is not kicking in erratically. It shouldn't completely cool down the full-hot airflow, but it will cool it. You can tell if the a/c unit is kicking in as you'll hear the compressor clutch kick in and the engine revs/sound will change under the load. If this is the case look for a short in the a/c wiring.
Hope this helps, and please rate my answer.

Dec 31, 2008 | 1994 Geo Tracker

Not finding what you are looking for?
1990 Geo Tracker Logo

180 people viewed this question

Ask a Question

Usually answered in minutes!

Top Geo Experts


Level 3 Expert

80608 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22326 Answers

Mike Gilbreath

Level 1 Expert

50 Answers

Are you a Geo Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides