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Discussion Starter · #1 ·
My 90 LX has a funny "hesitation" or "surge" around 1800 rpms. I feel it when driving at a steady speed in any gear at that rpm range. It is not very severe, just annoying. I used a code scanner, nothing came up except a code for the a/c switch or something. Thanks for any help!
 

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Discussion Starter · #2 ·
ttt

OK, this has gotten worse, you can really feel it between 1700 and 2200 rpms. Pulled codes again, now I have a code for the coolant temp sensor...Mileage is hurting, but doesn't smell rich or smoke. Mass air meter wires are clean, tb is clean (about 2000 miles old). Any ideas?

Thanks!

:confused: :mad:
 

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How's your engine temperature? Any chance that your thermostat is not allowing the engine to reach the proper 195 degrees operating temp? If the coolant sensor is indeed bad, or if the engine just actually never comes to proper full temperature, it will continue to run in an overly-rich warmup mode as the computer "thinks" that the engine is still warming up. This would cause both the surging and poor mileage you describe.

Steve A.
 

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Discussion Starter · #4 · (Edited)
amossm said:
How's your engine temperature? Any chance that your thermostat is not allowing the engine to reach the proper 195 degrees operating temp? If the coolant sensor is indeed bad, or if the engine just actually never comes to proper full temperature, it will continue to run in an overly-rich warmup mode as the computer "thinks" that the engine is still warming up. This would cause both the surging and poor mileage you describe.

Steve A.
Thanks Steve! BTW, do you go to the Car Craft Summer Nationals at the fairgrounds in July?

I'll change the sensor. The temp guage does look low, but I didn't think it would make the car do that.
 

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If the temperature gauge stays pretty low all the time, I'd bet that the coolant temperature sensor isn't bad but rather that the thermostat is not allowing the engine to warm up to full temperature. I'd probably try replacing the thermostat first (use a Motorcraft or good quality, brand name 195 degree thermostat). If that doesn't do it, then I'd go for the sensor replacement.

Steve A.
 

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Discussion Starter · #6 ·
I finally have had time to replace the temp sensor and the thermostat and I had the battery unhooked several times. The car now warms up on the guage and did not before, but still has the problem desribed above. Any other ideas? I am going to scan for codes again tomorrow.
 

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What other mods do you have? I think you're screwed with the other 50,000 people on this site. I want Ford to find out exactly what is causing this "surge" and "bucking" at a steady and relatively low rpm. Mine did it worst at 1000-1200 rpms when I was driving at a constant speed and rpm. I had earlier changed my O2 sensors to new Bosch replacement sensors, but I also changed heads, exhaust, and cam at the same time. I thought one of these other mods was causing my problems. I finally changed back to the 95,000 mile stock sensors and this helped the problem more than anything I have ever done. I'm don't know why, but it helped alot. Now, it only surges at extremely low rpm's (300-500), and I think even stock 5.0's will do that if you let them lug down that low. You might try the oxygen sensors; I won't promise it will cure your blues, but it definitely helped my car.
 

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Discussion Starter · #8 ·
This is probablythe single biggest problem with these cars, 100s of threads on this subject, it doesn't seem to have one answer.

I have had the surging idle for a while, but I can deal with it...Today I drove the car around 40 miles in town, never had the surging idle, but the bucking is between 1500 & 2200 rpms, but it is not there all the time. (not as noticable as before)

My mods are...65mm FMS T-Body, 73mm C&L Mass Air, BBK shorties, MAC Pro Cahmber, Flowmasters, Crane PS-92 coil, FMS 9mm plug wires, & don't forget the K&N.

It really felt better today, I'm driving it to work tomorrow & I'll see how it feels & then scan the codes- the Check Engine light is on after 10 minutes or so of driving, only seems to come on after higher RPMs are seen.

Anyone got an idea???

Thanks!!!
 

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Unstang said:
OK, this has gotten worse, you can really feel it between 1700 and 2200 rpms. Pulled codes again, now I have a code for the coolant temp sensor...Mileage is hurting, but doesn't smell rich or smoke. Mass air meter wires are clean, tb is clean (about 2000 miles old). Any ideas?

Thanks!

:confused: :mad:
I have the exact same problem. Starts bucking in that RPM range and throws and ECT code. I just changed the damn ECT sensor. Further I don't think it is realted to the engine not getting up to temp because I get the bucking whether the car is warm or not. The problem really started after I did a cam and intake swap.

I just tried removing my EGR vaccume line. I haven't gotten a chance to test it though because I'm snowwed in. I've adjusted the TPS voltage and cleaned the MAF, so those options are gone. I've also checked fuel pressure and monkeyed with timing. No luck there.
 

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ChrisRed89LX said:
I have the exact same problem. Starts bucking in that RPM range and throws and ECT code. I just changed the damn ECT sensor. Further I don't think it is realted to the engine not getting up to temp because I get the bucking whether the car is warm or not. The problem really started after I did a cam and intake swap.
My bet is it is lean. After a cam swap, and intake, what was done to adjust the turn on time of the Injectors to compensate for fuel at that area?
 
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