97 xj 4.0 Aw4.... Have an issue where I'm driving at any speed and the jeep feels like it loads up... Give it more throttle and it clears up for a sec then starts to bog agian..... Check engine light is on but a scanner wont read the obd port.... Been this way for a while.... Light has been on for a while which I thought was caused by speedo stopped working..... Today i did a full tune-up to it and replaced the tps and no change.... If I'm at full throttle it rums fine.... It does it worst when its cold...... I have a cracked header.... Would a exhaust leak cause this? My next idea was to replace the Cps...... Any imputed would be great....