check engine light/rpm tach

So my rpm tach is going crazy on my 93 mustang, its reading extremely low, like 800 when im going like 30mph and then it'll shoot up to like 2500. When it was running low my check engine light was also on, but it turns itself off after every once in a while but generally stays on. Today while stopping at a stop sign the idle was going crazy and it almost died on me. Also last week when I put fuel injector cleaner in it it actually helped with the rpm and check engine light. My friend thinks it might be an 02 sensor, or could it be from spark plugs? Also I was thinking maybe of getting an engine code reader cause they seem to be just about as much as bringing it in to get read, so if so are they easy to hook-up and any suggestions? (preferably a pretty cheap 1)

go to auto zone, u can use a code reader for free.

make absolutely sure that the connection on yoru iginition coil is totally clean and secure. that connection not only feeds voltage to the coil, but the grounds also signal the tach and feed the computer an RPM signal. the comp needs that signal to control ignition timing and fuel consumption, among other things. if that connection is dirty or loose, the signal is often interrupted, causing a check engine light.

do u ever use octane booster? if so u might need to change your spark plugs and ur ignition coil. its complicated if i can find the article about it ill post it.

i found the article its here
http://www.motorage.com/motorage/article/articleDetail.jsp?id=68245

thx for relpys guys, heres wat i got
Hey, thanks for the help. The nearest autozone is a good 25 minutes away and I'm not sure if my car would make it, but I bought one from a store for only $30. So I tested with keyonengine off and got : 157 - Mass Air Flow sensor fault; low voltage, 158- Mass Air Flow sensor fault, high voltage 223 - DIS- loss of dual plug inhibit (DPI) control, 224 - Erratic IDM input to provessor (all from cm). When I tried running it in engine on mode I got code 998, which my manual says my vehicle is iperating in failure mode, it goes into faulure mode when it detects a signal from a sensor that indicated the sensor has failed and is completely out of specifications. the comp substitues a fixed signal value for the failed sensor to keep the vehicle running.

Do these give you any ideas? Think maybe it is the MAF sensor? Also I don't think the spark plugs have been changed in a while, think it could maybe be those? Thanks for the help, I appreciate it.

thx for relpys guys, heres wat i got
Hey, thanks for the help. The nearest autozone is a good 25 minutes away and I'm not sure if my car would make it, but I bought one from a store for only $30. So I tested with keyonengine off and got : 157 - Mass Air Flow sensor fault; low voltage, 158- Mass Air Flow sensor fault, high voltage 223 - DIS- loss of dual plug inhibit (DPI) control, 224 - Erratic IDM input to provessor (all from cm). When I tried running it in engine on mode I got code 998, which my manual says my vehicle is iperating in failure mode, it goes into faulure mode when it detects a signal from a sensor that indicated the sensor has failed and is completely out of specifications. the comp substitues a fixed signal value for the failed sensor to keep the vehicle running.

Do these give you any ideas? Think maybe it is the MAF sensor? Also I don't think the spark plugs have been changed in a while, think it could maybe be those? Thanks for the help, I appreciate it.

change your plugs, that's a big one.

When you trouble shoot code always start with the lowest number code.
Bad spark plugs will not cause a MAF fault Code.
You should phyiscaly unplug the MAf and check all the wires first, for breaks, dirty, etc.

But the best way is to get a Mitchel on demand, or Mitchell manual, or Alldata (NOT A CHILTON OR HAYNES :) )
and follow the flow chart for a MAF fault.

You could try a different MAF, but If you don't do the flow chart trouble shooting, it's a shame to just throw parts at it and hope you hit something...

*What size Engine is in it ??*

So my rpm tach is going crazy on my 93 mustang, its reading extremely low, like 800 when im going like 30mph and then it'll shoot up to like 2500. )

This isn't a dual spark 2.3 by chance is it ? I'm not sure when they stopped making it .

If it is pull the spark plug wires off one at a time ( or use an inductive pick up) on the Right bank and check for spark,
then the left. More noticeable when the engine is hot.

If you are not getting spark on any of the plugs, your Ignition module is most likely shot - Big old thing looks like two regular modules glued together.

Big hint on when they go bad- It drives the signal to the tach... :iceslolan

it's a 2.3l, but wouldn't I need them to spark for the car to even start up? thanks for advice too, im going to try and get one of those torx bits and clean the MAF

it's a 2.3l, but wouldn't I need them to spark for the car to even start up? thanks for advice too, im going to try and get one of those torx bits and clean the MAF


The car will start and run if the secondary, (Drivers Side) is kaput. You will just get a Check Engine Light.

Not sure about the primary. What happens is only half the module is failing. I'm just going by my you said with the tach like 'quitting' and the dual spark error.

If you are not getting spark on 1 or more cylinders on one side, remember which one are not getting spart and test again later. Bet the dead spark moves around.

People will tell you its the one of the coils, if one bank is bad, but you can switch the coils ( They are the same) and wow look, now the OTHER coil is bad = Module is shot .

I'd check this first and then worry about the MAF, Cars don't like it when only 1/2 the plugs are firing, even though I don't think it'll cause a MAF error...

Let me know what happens I like fixing things that I had to find out by my self, when the guys at Ford can't fix it :)

well this is kinda weird, last nite I went to see how the car was running to see if it was going to be able to get me to work today and it ran perfectly fine, same today, idle is all good and rpm tach is too, check engine light is still on though but now it's only giving me the 157 error. so i dont kno if maybe when I was checking the connections if one of them was bad but now it seems like maybe the only thing left is the MAF sensor? Or at least I hope so... lol, but yeh once i get the time and a little help from a friend I'm going to look into the things tomminajar mentioned.

Learn anything new, or are you driving it till it stops running ? ;)

well actually I just got my enw maf sensor in mail today and installed that puppy. it was late so didn't get much of a chance to test car out but so far it definitly helped in the idle and the feeling it's going to stall at a stop. rpm tach is still messed tho and im still getting 224 error - Erratic IDM input to processor. I've been trying to read up on this on internet and from what I've read it seems like it's the coil? But don't worry tomminajar I'm going to take your advice to test out the module like you suggested I just gotta get some help from a friend first. Most likely saturday night. Thx for help guys, appreciate it. Any other ideas are welcome.